Fix rpc.control metrics and reduce object creation

[dapplion]

Metrics show that every RPC message we sent has a control in it, while only 0.02 received messages have a control. As shown with

rate(gossipsub_rpc_sent_control_total[$__rate_interval])
/
rate(gossipsub_rpc_sent_count_total[$__rate_interval])

The cause is that the control object is always created even when not necessary.

Description

• Create control object only when necessary
• Register control message when at least one array has at least one element

[codecov-commenter]

Codecov Report

Merging #230 (00b24f2) into master (fe07f20) will decrease coverage by 0.13%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##           master     #230      +/-   ##
==========================================
- Coverage   79.05%   78.91%   -0.14%     
==========================================
  Files          24       24              
  Lines        7662     7661       -1     
  Branches      765      802      +37     
==========================================
- Hits         6057     6046      -11     
- Misses       1605     1615      +10     

Impacted Files	Coverage Δ
ts/metrics.ts	22.94% <0.00%> (-0.14%)	⬇️
ts/index.ts	87.54% <25.00%> (-0.24%)	⬇️
ts/utils/create-gossip-rpc.ts	100.00% <100.00%> (ø)

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