Expose Vertx core metrics in Prometheus format

[pierDipi]

This PR exposes Vertx core metrics in Prometheus format and add
notes on how to configure Prometheus to scrape data plane pods.

Spec metrics in a separate PR.

Signed-off-by: Pierangelo Di Pilato pierangelodipilato@gmail.com

Part of #227

Proposed Changes

• Expose Vertx core metrics in Prometheus format

Prometheus dashboard

Release Note

- 🎁 Add new feature
Data plane pods expose server and client metrics in Prometheus format.

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pierDipi

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• OWNERS [pierDipi]

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[mattmoor]

Produced via:
prettier --write --prose-wrap=always $(find -name '*.md' | grep -v vendor | grep -v .github | grep -v docs/cmd/)

[pierDipi]

Waiting for the release!
/hold

[codecov]

Codecov Report

Merging #231 into master will decrease coverage by 0.03%.
The diff coverage is 53.84%.

@@             Coverage Diff              @@
##             master     #231      +/-   ##
============================================
- Coverage     76.44%   76.40%   -0.04%     
- Complexity      166      170       +4     
============================================
  Files            48       49       +1     
  Lines          1401     1420      +19     
  Branches         46       46              
============================================
+ Hits           1071     1085      +14     
- Misses          261      266       +5     
  Partials         69       69              

Flag	Coverage Δ	Complexity Δ
#java-unittests	76.25% <53.84%> (-0.08%)	170.00 <4.00> (+4.00)	⬇️
#unittests	76.40% <53.84%> (-0.04%)	170.00 <4.00> (+4.00)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
...knative/eventing/kafka/broker/dispatcher/Main.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...v/knative/eventing/kafka/broker/receiver/Main.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...ka/broker/core/metrics/MetricsOptionsProvider.java	88.88% <88.88%> (ø)	1.00 <1.00> (?)
...tive/eventing/kafka/broker/core/utils/BaseEnv.java	100.00% <100.00%> (ø)	7.00 <3.00> (+3.00)

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[mattmoor]

Produced via:
prettier --write --prose-wrap=always $(find -name '*.md' | grep -v vendor | grep -v .github | grep -v docs/cmd/)

[pierDipi]

/cc slinkydeveloper

[slinkydeveloper]

/lgtm

[pierDipi]

/unhold