Introduce techdocs metadata in techdocs-common

* Add TechdocsMetadata type in backend plugin endpoint
 * Introduce TechDocsMetadata type in frontend
 * Add changeset
 * Remove old thennable metadata resp
 * Address PR feedback
  - Remove explicit type annotation on TechDocsMetadata
  - Reintroduce res.send instead of throwing an error
  - Change logger info to logger error
 * Add TechDocsMetadata type in frontend plugin
 * Commit yarn.lock
 * Introduce JSON5 and remove parsing in local pub
Signed-off-by: Matei David <matei.david.35@gmail.com>

packages/techdocs-common/package.json

@@ -50,6 +50,7 @@
     "fs-extra": "^9.0.1",
     "git-url-parse": "^11.4.3",
     "js-yaml": "^4.0.0",
+    "json5": "^2.1.3",
     "mime-types": "^2.1.27",
     "mock-fs": "^4.13.0",
     "recursive-readdir": "^2.2.2",