docs: clarify username formats, ProjectLeader-as-group, and filter special-char behavior

[jacalata]

Closes #993, #1067, #1200.

Motivation

Three long-standing stale issues, all traceable to gaps in the same doc
region:

• Update docs and examples to properly show required fields for adding new users #993: users.add docstring gave no hint that name is the server-side
  authentication identifier, not the person's display name. The primary
  example TSC.UserItem('new_user', ...) misleads readers into treating it
  as a display-name field.
• Clarify/write docs for assigning a group as Project Leader (permissions) #1067: projects.update_permissions had no examples, so callers had no
  guide for the common "assign a group as Project Leader" case.
• workbook filter fails with special characters.  #1200: The REST filter grammar treats ,, &, :, [, ] as
  delimiters and the server does not support escaping, but nothing in the
  docstring warned about this or documented the wildcard workaround.

Behavior change

Docs only. No API change.

• UserItem.name + users.add docstrings describe the required format per
  auth scheme: Cloud = email, local Server = username, AD-backed =
  SAMAccountName@FullyQualifiedDomain or UPN. Example split into Cloud +
  AD invocations.
• projects.update_permissions example constructs a PermissionsRule
  with grantee=<group> and capability=ProjectLeader, plus a note that
  update_permissions fully replaces existing rules (call
  populate_permissions first if preserving).
• Filter class + QuerySet.filter docstrings document the reserved
  delimiter characters and the *-wildcard workaround under the Equals
  operator, citing the server version requirement (Tableau Cloud May 2023
  or Tableau Server 2022.1.14) sourced from the public "Filtering and
  Sorting" REST API docs.

Test plan

• test/test_user.py, test_user_model.py, test_project.py,
  test_project_model.py, test_filter.py: 89 passed
• mypy clean

🤖 Generated with Claude Code

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
tableauserverclient
__init__.py	5	0	100%
config.py	15	0	100%
datetime_helpers.py	25	1	1	96%
exponential_backoff.py	20	0	100%
filesys_helpers.py	31	0	100%
namespace.py	26	3	3	88%
tableauserverclient/bin
__init__.py	2	0	100%
_version.py	358	212	212	41%
tableauserverclient/helpers
__init__.py	1	0	100%
logging.py	2	0	100%
strings.py	31	1	1	97%
tableauserverclient/models
__init__.py	46	0	100%
collection_item.py	41	7	7	83%
column_item.py	55	32	32	42%
connection_credentials.py	35	11	11	69%
connection_item.py	94	14	14	85%
custom_view_item.py	144	21	21	85%
data_acceleration_report_item.py	54	1	1	98%
data_alert_item.py	158	4	4	97%
data_freshness_policy_item.py	155	15	15	90%
database_item.py	207	36	36	83%
datasource_item.py	300	12	12	96%
dqw_item.py	104	5	5	95%
exceptions.py	4	0	100%
extensions_item.py	132	4	4	97%
extract_item.py	44	4	4	91%
favorites_item.py	69	8	8	88%
fileupload_item.py	19	0	100%
flow_item.py	149	10	10	93%
flow_run_item.py	71	0	100%
group_item.py	89	6	6	93%
groupset_item.py	49	7	7	86%
interval_item.py	182	32	32	82%
job_item.py	192	10	10	95%
linked_tasks_item.py	79	1	1	99%
location_item.py	29	2	2	93%
metric_item.py	129	13	13	90%
oidc_item.py	63	3	3	95%
pagination_item.py	34	1	1	97%
permissions_item.py	111	12	12	89%
project_item.py	207	31	31	85%
property_decorators.py	100	18	18	82%
reference_item.py	26	2	2	92%
revision_item.py	59	1	1	98%
schedule_item.py	209	6	6	97%
server_info_item.py	37	7	7	81%
site_item.py	636	13	13	98%
subscription_item.py	101	2	2	98%
table_item.py	119	18	18	85%
tableau_auth.py	61	25	25	59%
tableau_types.py	27	1	1	96%
tag_item.py	15	0	100%
target.py	6	0	100%
task_item.py	56	2	2	96%
user_item.py	310	18	18	94%
view_item.py	220	16	16	93%
virtual_connection_item.py	64	8	8	88%
webhook_item.py	69	1	1	99%
workbook_item.py	362	16	16	96%
tableauserverclient/server
__init__.py	9	0	100%
exceptions.py	4	0	100%
filter.py	29	1	1	97%
pager.py	33	1	1	97%
query.py	143	15	15	90%
request_factory.py	1335	195	195	85%
request_options.py	386	5	5	99%
server.py	188	23	23	88%
sort.py	6	0	100%
tableauserverclient/server/endpoint
__init__.py	35	0	100%
auth_endpoint.py	77	11	11	86%
custom_views_endpoint.py	152	12	12	92%
data_acceleration_report_endpoint.py	21	0	100%
data_alert_endpoint.py	94	23	23	76%
databases_endpoint.py	111	30	30	73%
datasources_endpoint.py	323	33	33	90%
default_permissions_endpoint.py	44	3	3	93%
dqw_endpoint.py	45	16	16	64%
endpoint.py	212	20	20	91%
exceptions.py	77	6	6	92%
extensions_endpoint.py	31	0	100%
favorites_endpoint.py	94	22	22	77%
fileuploads_endpoint.py	51	0	100%
flow_runs_endpoint.py	62	9	9	85%
flow_task_endpoint.py	21	2	2	90%
flows_endpoint.py	198	53	53	73%
groups_endpoint.py	126	9	9	93%
groupsets_endpoint.py	72	7	7	90%
jobs_endpoint.py	67	9	9	87%
linked_tasks_endpoint.py	37	0	100%
metadata_endpoint.py	88	14	14	84%
metrics_endpoint.py	55	6	6	89%
oidc_endpoint.py	42	1	1	98%
permissions_endpoint.py	44	3	3	93%
projects_endpoint.py	178	24	24	87%
resource_tagger.py	127	35	35	72%
schedules_endpoint.py	119	11	11	91%
server_info_endpoint.py	36	10	10	72%
sites_endpoint.py	130	27	27	79%
subscriptions_endpoint.py	56	14	14	75%
tables_endpoint.py	110	36	36	67%
tasks_endpoint.py	63	6	6	90%
users_endpoint.py	183	8	8	96%
views_endpoint.py	150	9	9	94%
virtual_connections_endpoint.py	113	10	10	91%
webhooks_endpoint.py	54	9	9	83%
workbooks_endpoint.py	338	22	22	93%
TOTAL	12007	1423	88%