(PXP-6469): Limit service account to six projects per account

[BinamB]

Trying to register too many projects to a single google service account at once returns a timeout error from Fence.

Bug Fixes

• Limit service accounts to 6 projects and added a 400 status code if attempt to register more. PXP-5889

Improvements

• Added unit tests to test 6 project limit in the POST and PATCH /google/service_accounts endpoints
• Parameterized the limit of projects a service account can have as SERVICE_ACCOUNT_LIMIT in config-default.yaml.

[github-actions]

The style in this PR agrees with black. ✔️

This formatting comment was generated automatically by a script in uc-cdis/wool.

[coveralls]

Pull Request Test Coverage Report for Build 9543

• 7 of 8 (87.5%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 69.209%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
fence/blueprints/google.py	7	8	87.5%

Totals
Change from base Build 9540:	0.02%
Covered Lines:	5345
Relevant Lines:	7723

---

💛 - Coveralls