Support fatjar packaging by consolidating `plugin.yml` resources

[qodo-code-review]

Description:

• The plugin is being packaged as a single “fatjar” artifact, so plugin metadata must be packaged consistently in one place.
• Having multiple version-specific plugin.yml files (e.g., under src/b1_7_3/resources/ and src/r1_21/resources/) can lead to duplicate/incorrect plugin descriptors in the final jar.
• Placeholder plugin.yml content increases the risk of shipping invalid metadata (e.g., incorrect main, name, or api-version).
• Build output should reliably include exactly one valid plugin descriptor for the runtime platform to load.

Deliverables:

• Remove duplicates: Eliminate the version-specific plugin.yml resources from src/b1_7_3/resources/ and src/r1_21/resources/ to prevent multiple descriptors being packaged.
• Single source: Ensure the fatjar build produces one authoritative plugin.yml in the final artifact (from the intended shared location or build-generated source).
• Valid metadata: Confirm the packaged plugin.yml contains correct plugin metadata (name, version, main class, api version) and is not placeholder content.