chore(ai-agents): trim supportedHostedAgentRegions list

[antriksh30]

Trims the supportedHostedAgentRegions allow-list in init_locations.go (used by azd ai agent init for the location prompt and model-location filter). Removes: canadaeast, centralus, eastus, germanywestcentral, italynorth, southcentralus, uaenorth, uksouth, westeurope.

[Copilot]

Pull request overview

This PR trims the hardcoded supportedHostedAgentRegions allow-list used by the azure.ai.agents extension during azd ai agent init to constrain both the location prompt and the model-location filtering to the currently supported hosted-agent regions.

Changes:

• Removed 9 Azure regions from the supportedHostedAgentRegions hardcoded list.
• Narrowed the effective region set used by supportedRegionsForInit() and supportedModelLocations().

[Copilot]

This change removes eastus (and other regions) from the allow-list, but init_locations_test.go still treats eastus as supported (e.g., AllSupported / SomeUnsupported). As-is, go test will fail; update those test cases to use a currently-supported region (e.g., eastus2) and adjust the expected lengths accordingly.

[jongio]

CI is failing on all three platforms - the tests in init_locations_test.go use eastus (which this PR removes) as test data. The AllSupported and SomeUnsupported cases need their inputs swapped to a region that remains in the list (e.g., eastus2). The mutation test on line 74 should be updated too.

Separate question: the code comment on line 8-9 references the hosted agents region docs, which currently lists only 4 regions (Australia East, Canada Central, North Central US, Sweden Central). After this PR, the list still has 18 regions. Is the code tracking a different/internal source, or are there more regions to trim? Might be worth updating the comment to point at the actual source if it's different from the public docs.

[trangevi]

This should be closed in favor of #7930

[antriksh30]

closed in favor of #7930