[P0] Codeowners metadata fields

Service label info:
* ServiceLabel

Codeowners:
* Service Tree Dev Owner (from Service Tree) -- Fallback if package doesn't have owners
* Service Tree PM owner (from Service Tree) -- Fallback if no dev owners
* Codeowner GitHub handle -- Correlate with open source
* Codeowner MS alias --
* team alias -- Is this GitHub team or MSFT alias?

Package item information:
* SDK source code directory (e.g. /sdk/confidentialledger/azure-confidentialledger/)
* API spec path

Note: Folder paths may be different per repo. There is no intent to unify folder paths with this initiative. This new source of truth should track paths for each language.