feat!: remove label keys as they are no longer part of the spec

[naseemkullah]

Which problem is this PR solving?

• Remove labelKeys from metric creation #1119

Short description of the changes

• Removed or replaced all occurrences of labelKeys

• Removed or replaced all occurrences of prom-clients's labelValues

• Removed no longer used private _getLabelValues()

• All metrics now have all labels associated to them, tests adjusted accordingly

[codecov]

Codecov Report

Merging #1126 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1126      +/-   ##
==========================================
- Coverage   92.32%   92.31%   -0.02%     
==========================================
  Files         116      116              
  Lines        3402     3395       -7     
  Branches      689      688       -1     
==========================================
- Hits         3141     3134       -7     
  Misses        261      261              

Impacted Files	Coverage Δ
packages/opentelemetry-api/src/metrics/Metric.ts	100.00% <ø> (ø)
packages/opentelemetry-metrics/src/Metric.ts	100.00% <ø> (ø)
packages/opentelemetry-metrics/src/export/types.ts	100.00% <ø> (ø)
packages/opentelemetry-metrics/src/types.ts	100.00% <ø> (ø)
...pentelemetry-exporter-prometheus/src/prometheus.ts	91.39% <100.00%> (-0.61%)	⬇️
...ckages/opentelemetry-metrics/src/export/Batcher.ts	100.00% <100.00%> (ø)

[mayurkale22]

Added a few comments.

[mayurkale22]

Are you planning to update examples (https://github.com/open-telemetry/opentelemetry-js/blob/master/examples/prometheus/index.js#L23) in separate PR?

[naseemkullah]

Are you planning to update examples (https://github.com/open-telemetry/opentelemetry-js/blob/master/examples/prometheus/index.js#L23) in separate PR?

Ah, no, will do it here, thanks.

edit: done

[mayurkale22]

@open-telemetry/javascript-approvers would like to get more reviews on this.

[obecny]

out of curiosity, how am I able to create a labels at this moment after this change. What would be a correct way of doing it now, if for any reason I want to have labels ?

[dyladan]

You can't. Labels are now applied only by binding them to an instrument, or calling the instrument method with labels as the second argument like add(10, { core: 1 })

[vmarchaud]

lgtm

[obecny]

lgtm