chore(github): convert `graphql_rate_limit` errors into a different error than `platform-unknown-error`

[jamietanna]

Via #44190

Trace logs for the platform-unknown-error case:

{"type":"RATE_LIMIT","code":"graphql_rate_limit","message":"API rate limit already exceeded for installation ID <redacted>"}

ERROR: Repository has unknown error  "platform-unknown-error"
    at getPlatformConfig (lib/workers/repository/init/apis.ts:96)
    at initRepo (lib/modules/platform/github/index.ts:575)

The getAppDetails / "Authentication failure" case shows the same graphql_rate_limit response on the viewer query.