Add support CLIENT KILL [MAXAGE]

[dengliming]

closes #2765

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[tishun]

@mp911de should we merge this one?

[mp911de]

I have a few changes to propose:

• Set @since tags to 7.0
• Improve the test arrangement as a Redis node can have multiple inactive clients. We should be able to clearly identify the clients to disconnect

Other than that, it's fine to merge this PR.

[tishun]

@dengliming would you be able to address the changes @mp911de suggested?

[uglide]

LGTM