KafkaSource: expose dispatcher metrics and profiling data

[lionelvillard]

Proposed Changes

Release Note

🧽 The KafkaSource dispatchers now expose metrics and profiling information 

Docs

[codecov]

Codecov Report

Merging #221 (10d6edf) into master (4b0de1e) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #221      +/-   ##
==========================================
- Coverage   76.10%   75.97%   -0.14%     
==========================================
  Files         114      114              
  Lines        4395     4399       +4     
==========================================
- Hits         3345     3342       -3     
- Misses        851      858       +7     
  Partials      199      199              

Impacted Files	Coverage Δ
...rce/reconciler/source/resources/receive_adapter.go	100.00% <100.00%> (ø)
...el/distributed/dispatcher/dispatcher/dispatcher.go	66.05% <0.00%> (-6.43%)	⬇️

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[lionelvillard]

/assign @aliok

[aliok]

/lgtm
/approve

[knative-prow-robot]

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