chore: update README with plugins work and add DNS plugin in default …

[mayurkale22]

…supported plugins list

Which problem is this PR solving?

• Add a line about @opentelemetry/base package.

• Remove WIP from opentelemetry-exporter-prometheus package.

• Add WIP plugins (redis and mysql)

• Add DNS plugin in default supported plugins list

[codecov-io]

Codecov Report

Merging #529 into master will decrease coverage by 3.93%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #529      +/-   ##
==========================================
- Coverage   96.46%   92.53%   -3.94%     
==========================================
  Files         128      146      +18     
  Lines        6455     7168     +713     
  Branches      556      621      +65     
==========================================
+ Hits         6227     6633     +406     
- Misses        228      535     +307

Impacted Files	Coverage Δ
...telemetry-plugin-grpc/test/utils/assertionUtils.ts	100% <0%> (ø)	⬆️
.../opentelemetry-plugin-dns/test/utils/assertSpan.ts	100% <0%> (ø)	⬆️
...try-node/test/instrumentation/PluginLoader.test.ts	100% <0%> (ø)	⬆️
...try-plugin-dns/test/functionals/dns-enable.test.ts	100% <0%> (ø)	⬆️
...ckages/opentelemetry-exporter-zipkin/src/zipkin.ts	100% <0%> (ø)
...-document-load/src/enums/PerformanceTimingNames.ts	100% <0%> (ø)
...entelemetry-scope-zone-peer-dep/test/utils.test.ts	0% <0%> (ø)
...ages/opentelemetry-scope-zone-peer-dep/src/util.ts	100% <0%> (ø)
...-scope-zone-peer-dep/test/ZoneScopeManager.test.ts	0% <0%> (ø)
...ges/opentelemetry-exporter-zipkin/test/e2e.test.ts	100% <0%> (ø)
... and 20 more

[obecny]

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