Add 'count' option to the 'RANDOMKEY' command

[hwware]

Reference the issue redis/redis#11915 and #788
I would like to add one more option for RANDOMKEY command, allow user to get multiply random keys once.
It is similar to existing command ZRANDMEMBER key [count [WITHSCORES]] and SRANDMEMBER key [count]

The new command format as: RANDOMKEY [COUNT count]

If the provided count argument is positive, return an array of distinct elements.
If called with a negative count, the behavior changes and the command is allowed to return the same elements multiple times.

[codecov]

Codecov Report

Attention: Patch coverage is 68.18182% with 14 lines in your changes missing coverage. Please review.

Project coverage is 71.00%. Comparing base (2c9db1a) to head (e1dacbd).
Report is 14 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/db.c	68.18%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1847      +/-   ##
============================================
- Coverage     71.03%   71.00%   -0.03%     
============================================
  Files           123      123              
  Lines         65665    65710      +45     
============================================
+ Hits          46645    46660      +15     
- Misses        19020    19050      +30     

Files with missing lines	Coverage Δ
src/commands.def	100.00% <ø> (ø)
src/db.c	88.78% <68.18%> (-0.71%)	⬇️

... and 13 files with indirect coverage changes

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[madolson]

I'm still not inclined to accept this feature. I don't think it is really that useful.

[hwware]

I'm still not inclined to accept this feature. I don't think it is really that useful.

It is a very old requirement from Redis community, if recently there is no more people to care about it, I will close it later

[hwware]

There is no requirement recently, I decide to close this PR.