Expose Redis/RedisAI main thread cpu usage via modules info

[filipecosta90]

The following PR exposes the main thread CPU info via info modules ( linux systems only ). In that manner we will have:

• ai_self_used_cpu_sys and ai_self_used_cpu_user: which is the sum of resources used by all threads in the process
• ai_children_used_cpu_sys and ai_children_used_cpu_user: resource usage statistics for all of redis terminated child processes
• ai_main_thread_used_cpu_sys and ai_main_thread_used_cpu_user: resource usage statistics for the main thread which in this case is Redis/RedisAI main thread

Sample output:

$ redis-cli info modules
# Modules
module:name=ai,ver=999999,api=1,filters=0,usedby=[],using=[],options=[]

# ai_git
ai_git_sha:ffd7e8e7db02ba97d0472493d4dc626a2703eb09

# ai_load_time_configs
ai_threads_per_queue:1
ai_inter_op_parallelism:0
ai_intra_op_parallelism:0

# ai_cpu
ai_self_used_cpu_sys:9.682204
ai_self_used_cpu_user:150.129278
ai_children_used_cpu_sys:0.000000
ai_children_used_cpu_user:0.000000
ai_main_thread_used_cpu_sys:5.129278
ai_main_thread_used_cpu_user:2.682204
ai_queue_CPU_bthread_#1_used_cpu_total:0.000856

[codecov]

Codecov Report

Merging #530 (0d68a93) into master (665b358) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #530      +/-   ##
==========================================
+ Coverage   75.25%   75.29%   +0.04%     
==========================================
  Files          22       22              
  Lines        5217     5226       +9     
==========================================
+ Hits         3926     3935       +9     
  Misses       1291     1291              

Impacted Files	Coverage Δ
src/redisai.c	79.59% <100.00%> (+0.28%)	⬆️

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