Add GET /ui/connections/hook_meta/{connection_type} endpoint

[yuseok89]

Related: #61815

Add a new endpoint that returns metadata for a single connection type.
Unlike the existing GET /ui/connections/hook_meta which imports all hook classes (~129) to build the full list, this endpoint uses ProvidersManager._hooks_lazy_dict to import only the requested hook, significantly reducing response time for on-demand metadata lookup.
This is the first step toward improving the Add Connection page load time — load connection types first (lightweight), then load metadata only when the user selects a type.

Screenshots

Tested via curl in Breeze shell:

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[yuseok89]

The approach has changed. I'm closing this PR in favor of using provider.yaml metadata instead of adding new APIs. See the new implementation in #63826.