docs: add requires_billing, retire .cloud-repo-tools.json

[bcoe]

Adds the new requires_billing field, which allows us to toggle out sections of the README depending on whether a user needs to activate billing on their account to access the given service (see).

Given that this is the last piece of information we actively needed from .cloud-repo-tools.json, I'm killing this now unused meta-information file.

• 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 #644 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #644   +/-   ##
=======================================
  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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