[Client Introspection] Client Count Command

[sarthakaggarwal97]

With this PR, we would include a new subcommand called CLIENT COUNT.

This subcommand will be responsible for counting the number of clients, while supporting the existing filters and the newly added filters in #1466.

Sample Output:

127.0.0.1:6379> client list
id=8 addr=127.0.0.1:49924 laddr=127.0.0.1:6379 fd=8 name= age=1413 idle=933 flags=N db=0 sub=0 psub=0 ssub=0 multi=-1 watch=0 qbuf=0 qbuf-free=0 argv-mem=0 multi-mem=0 rbs=1024 rbp=0 obl=0 oll=0 omem=0 tot-mem=1920 events=r cmd=client|count user=default redir=-1 resp=2 lib-name= lib-ver= tot-net-in=380 tot-net-out=217586 tot-cmds=9
id=9 addr=127.0.0.1:49927 laddr=127.0.0.1:6379 fd=9 name= age=1411 idle=0 flags=N db=0 sub=0 psub=0 ssub=0 multi=-1 watch=0 qbuf=0 qbuf-free=0 argv-mem=10 multi-mem=0 rbs=1024 rbp=0 obl=0 oll=0 omem=0 tot-mem=1946 events=r cmd=client|list user=default redir=-1 resp=2 lib-name= lib-ver= tot-net-in=79 tot-net-out=216501 tot-cmds=2
id=10 addr=127.0.0.1:49928 laddr=127.0.0.1:6379 fd=10 name= age=1409 idle=1409 flags=N db=0 sub=0 psub=0 ssub=0 multi=-1 watch=0 qbuf=0 qbuf-free=0 argv-mem=0 multi-mem=0 rbs=1024 rbp=0 obl=0 oll=0 omem=0 tot-mem=1920 events=r cmd=command|docs user=default redir=-1 resp=2 lib-name= lib-ver= tot-net-in=27 tot-net-out=215501 tot-cmds=1
127.0.0.1:6379> client count
(integer) 3
127.0.0.1:6379> client count id 8 9
(integer) 2
127.0.0.1:6379> client count id 8 9 addr 127.0.0.1:49927
(integer) 1
127.0.0.1:6379> client count id 8 9 flags N
(integer) 2
127.0.0.1:6379> 

Built on top of: #1401, #1466
Resolves: #668

[codecov]

Codecov Report

Attention: Patch coverage is 86.94779% with 65 lines in your changes missing coverage. Please review.

Project coverage is 70.84%. Comparing base (b56f4f7) to head (e5c4782).
Report is 1 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/networking.c	86.94%	65 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1467      +/-   ##
============================================
- Coverage     70.86%   70.84%   -0.03%     
============================================
  Files           119      119              
  Lines         64693    64889     +196     
============================================
+ Hits          45847    45970     +123     
- Misses        18846    18919      +73     

Files with missing lines	Coverage Δ
src/commands.def	100.00% <ø> (ø)
src/networking.c	87.73% <86.94%> (-0.90%)	⬇️

... and 11 files with indirect coverage changes