PMM-15206: RTA host filter substring matching

[mattiasimonato]

Ticket number: PMM-15206

Feature build: SUBMODULES-4512

The Host column had no filterFn, so material-react-table used its fuzzy default and matched the typed value as a subsequence instead of a substring.
Setting filterFn: 'contains' makes Host behave like the Query column, which already used it.

[coderabbitai]

Walkthrough

Changes

Host filtering

Layer / File(s)	Summary
Host filter behavior and validation ui/apps/pmm/src/pages/rta/overview/table/OverviewTable.constants.tsx, ui/apps/pmm/src/pages/rta/overview/table/OverviewTable.test.tsx	The host column now uses filterFn: 'contains' instead of MRT’s default fuzzy filtering. Tests verify substring matching and case-insensitive matching.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the RTA host filter change and the new substring-matching behavior.
Description check	✅ Passed	The description includes the required ticket and feature build, and clearly explains the filter behavior change.

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