chore: add prometheus example

[dyladan]

Which problem is this PR solving?

• Example: Add basic metrics example with prometheus exporter #540

Short description of the changes

• Add prometheus metrics example

[codecov-io]

Codecov Report

Merging #560 into master will increase coverage by 0.34%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #560      +/-   ##
==========================================
+ Coverage   92.28%   92.63%   +0.34%     
==========================================
  Files         151      152       +1     
  Lines        7313     7740     +427     
  Branches      641      666      +25     
==========================================
+ Hits         6749     7170     +421     
- Misses        564      570       +6

Impacted Files	Coverage Δ
...opentelemetry-core/src/platform/node/timer-util.ts	33.33% <0%> (-16.67%)	⬇️
.../opentelemetry-plugin-redis/test/assertionUtils.ts	95.83% <0%> (-4.17%)	⬇️
...es/opentelemetry-node/src/instrumentation/utils.ts	96% <0%> (-4%)	⬇️
...res/opentelemetry-plugin-pg/test/assertionUtils.ts	96.29% <0%> (-3.71%)	⬇️
...ges/opentelemetry-core/src/common/ConsoleLogger.ts	91.66% <0%> (-3.08%)	⬇️
...ckages/opentelemetry-core/src/common/NoopLogger.ts	57.14% <0%> (-2.86%)	⬇️
...telemetry-core/src/context/propagation/B3Format.ts	96.15% <0%> (-1.29%)	⬇️
...entelemetry-exporter-jaeger/test/transform.test.ts	100% <0%> (ø)	⬆️
...entelemetry-core/test/common/ConsoleLogger.test.ts	100% <0%> (ø)	⬆️
...opentelemetry-base/test/resources/resource.test.ts	100% <0%> (ø)	⬆️
... and 31 more

[dyladan]

@mayurkale22 thanks for the suggestions. Can't believe I missed that.

[dyladan]

The failing test is lint & docs saying https://github.com/open-telemetry/opentelemetry-js is a 500 link. I think GitHub may be having issues.

[mayurkale22]

The failing test is lint & docs saying https://github.com/open-telemetry/opentelemetry-js is a 500 link. I think GitHub may be having issues.

Just restarted the workflow, hopefully that will solve the problem.