Feature COMMANDLOG to record slow execution and large request/reply

[soloestoy]

As discussed in PR #336.

We have different types of resources like CPU, memory, network, etc. The slowlog can only record commands eat lots of CPU during the processing phase (doesn't include read/write network time), but can not record commands eat too many memory and network. For example:

1. run "SET key value(10 megabytes)" command would not be recored in slowlog, since when processing it the SET command only insert the value's pointer into db dict. But that command eats huge memory in query buffer and bandwidth from network. In this case, just 1000 tps can cause 10GB/s network flow.
2. run "GET key" command and the key's value length is 10 megabytes. The get command can eat huge memory in output buffer and bandwidth to network.

This PR introduces a new command COMMANDLOG, to log commands that consume significant network bandwidth, including both input and output. Users can retrieve the results using COMMANDLOG get <count> large-request and COMMANDLOG get <count> large-reply, all subcommands for COMMANDLOG are:

• COMMANDLOG HELP
• COMMANDLOG GET <count> <slow|large-request|large-reply>
• COMMANDLOG LEN <slow|large-request|large-reply>
• COMMANDLOG RESET <slow|large-request|large-reply>

And the slowlog is also incorporated into the commandlog.

[codecov]

Codecov Report

Attention: Patch coverage is 88.18898% with 15 lines in your changes missing coverage. Please review.

Project coverage is 70.71%. Comparing base (2df56d8) to head (03a6736).
Report is 18 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/commandlog.c	92.79%	8 Missing ⚠️
src/server.c	57.14%	3 Missing ⚠️
src/latency.c	0.00%	2 Missing ⚠️
src/module.c	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1294      +/-   ##
============================================
+ Coverage     70.69%   70.71%   +0.01%     
============================================
  Files           114      115       +1     
  Lines         63161    63209      +48     
============================================
+ Hits          44650    44696      +46     
- Misses        18511    18513       +2     

Files with missing lines	Coverage Δ
src/blocked.c	91.90% <100.00%> (ø)
src/commands.def	100.00% <ø> (ø)
src/config.c	78.83% <ø> (ø)
src/server.h	100.00% <ø> (ø)
src/latency.c	80.87% <0.00%> (-0.05%)	⬇️
src/module.c	9.64% <0.00%> (-0.02%)	⬇️
src/server.c	87.67% <57.14%> (-0.02%)	⬇️
src/commandlog.c	92.79% <92.79%> (ø)

... and 21 files with indirect coverage changes

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[hwware]

Just for Note: Let's first refresh the memory in pr #336, the last comment conclusion is:

After a core team meeting, we decided adding a new command COMMANDLOG with subcommands HEAVYTRAFFIC and SLOW, and then slowlog.c can be renamed to a common commandlog.c. #336 (comment)

[hwware]

From my understanding, for the command: commandlog get should be:
COMMANDLOG get count slow | heavytraffic-input | heavytraffic-output.

commandlog len should be:
COMMANDLOG len slow | heavytraffic-input | heavytraffic-output.

commandlog reset should be:
COMMANDLOG reset slow | heavytraffic-input | heavytraffic-output.

Can you describe the terms heavytraffic-input and heavytraffic-output in the json file (argument part) because I can only know
them from the source codes and valkey.conf so far?

And I think the existing slowlog commands should be deprecated? If yes, I think you should update the related json files as well.

[hwware]

LGTM, approved