[FEATURE] add test connection button to prometheus plugin

[adrianSepiol]

Related pull requests (in order):

1. [BUGFIX] set correct ContentLength for request body perses#4007
2. [FEATURE] Add test datasource connection button shared#99
3. This one
4. [BREAKINGCHANGE] Replace local buildProxyUrl with shared implementation from @perses-dev/client perses#4302
5. This one

Related issue:
perses/perses#1542

Description

Uses "/api/v1/status/buildinfo" instead of "/-/healthy" because from what I tested and found out, the config for CORS on prometheus side is applied on "/api/*" path. So by using "/-/healthy" the direct access test connection would not work.

Screenshots

Edit:

Screen.Recording.2026-07-27.at.17.31.05.mov

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• All commits have DCO signoffs.

UI Changes

• Changes that impact the UI include screenshots and/or screencasts of the relevant changes.
• Code follows the UI guidelines.