feat: add support for custom grants

[raffis]

Current situation

With postgres v14 the public schema is locked. Meaning permission needs to be set explicitly.

Proposal

Extend the PostgreSQLUser CRD with grants and roles. While grants gets a default rule which adds access to the public schema
if not defined otherwise.
With roles one can grant custom roles to the user (GRANT role to user).

[github-actions]

Pull Request Test Coverage Report for Build 5222626638

• 29 of 29 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.4%) to 74.648%

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Totals
Change from base Build 5175076832:	1.4%
Covered Lines:	583
Relevant Lines:	781

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💛 - Coveralls