Add authentication options to the DocFX code snippets

[bernardnormier]

Fixes #4823.

The DocFX code snippets that create a Server passed no server authentication options, and the default transport
(QUIC) requires a server certificate. The snippets that create a ClientConnection to icerpc://localhost passed no
client authentication options either, so they built but could not connect.

This PR applies the pattern of the src README samples to all 16 regions: the server regions load the test server
certificate and pass serverAuthenticationOptions, and the client regions load the test root CA and pass
clientAuthenticationOptions. Both call the CreateServerAuthenticationOptions /
CreateClientAuthenticationOptions helpers from examples/common/Program.Authentication.cs, which the docfx example
projects now compile in, so the snippets stay in sync with the real helpers. A single two-line comment explains why
the certificate is there and where the helper lives, and the Server / ClientConnection construction itself carries
no comment.

Two pre-existing slips in CompressorMiddlewareExamples.cs are fixed along the way: the middleware region created an
unused client connection, and the file was in the IceRpc.Telemetry.Examples namespace.

What's Changed

None — DocFX code snippets only.

🤖 Generated with Claude Code

[InsertCreativityHere]

Looks good to me!

[InsertCreativityHere]

Seems like this name MetricsMiddlewareExamples is a leftover copy-paste.
This isn't introduced by your PR, but thought I'd point it out since we're touching this code anyways.

[bernardnormier]

Good catch, fixed in 1a55a8e.