feat: add redis sentinel master config

[opan]

Expose couple new metrics to show current redis sentinel master config, such as quorum, parallel-syncs, failover-timeou, and down-after-milliseconds. As of now, I have only expose these 4 settings. We can add more if needed.

Thank you

[coveralls]

Pull Request Test Coverage Report for Build 224

• 14 of 14 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 92.203%

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Totals
Change from base Build 221:	0.2%
Covered Lines:	1963
Relevant Lines:	2129

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💛 - Coveralls

[oliver006]

👍

Thanks for the PR!

Is it worth adding a few tests for this to check the metrics show up?

[opan]

Sure, I can add some test for this.