docs: add a .repo-metadata.json

[bcoe]

I'm using nodejs-storage to test our new synthtool README generation, it relies on @busunkim96's meat-information work.

• Tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

[codecov]

Codecov Report

Merging #639 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #639   +/-   ##
=======================================
  Coverage   97.94%   97.94%           
=======================================
  Files           9        9           
  Lines         874      874           
  Branches       99       99           
=======================================
  Hits          856      856           
  Misses          9        9           
  Partials        9        9

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