docs: Change term "Master" to "primary" or "leader"

[jchancojr]

Change the term "master" to either "primary" or "leader" for PostgreSQL and Patroni respectively. I've left the release notes alone to preserve release history.

[jchancojr]

Fixes #2414

[jchancojr]

Thanks very much @CyberDem0n

Let me know if there's anything else I missed.

[coveralls]

Pull Request Test Coverage Report for Build 3114622661

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.883%

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Totals
Change from base Build 3081285508:	0.0%
Covered Lines:	11129
Relevant Lines:	11142

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💛 - Coveralls

[CyberDem0n]

:+1:

[hughcapet]

👍

[CyberDem0n]

Merged, thank you @jchancojr, @cbandy, @hunleyd