chore: moving plugin from api to core

[obecny]

Which problem is this PR solving?

• Fixes Move plugin interfaces out of API package #1710

Short description of the changes

• Move plugin interfaces out of API package

[codecov]

Codecov Report

Merging #1715 (9f50196) into master (86cbd67) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1715   +/-   ##
=======================================
  Coverage   91.35%   91.35%           
=======================================
  Files         165      165           
  Lines        5138     5138           
  Branches     1056     1056           
=======================================
  Hits         4694     4694           
  Misses        444      444           

Impacted Files	Coverage Δ
...ntelemetry-core/src/platform/BaseAbstractPlugin.ts	60.00% <ø> (ø)
...opentelemetry-core/src/platform/node/BasePlugin.ts	81.08% <ø> (ø)
...telemetry-node/src/instrumentation/PluginLoader.ts	93.82% <ø> (ø)
packages/opentelemetry-plugin-fetch/src/fetch.ts	96.55% <ø> (ø)

[Flarna]

Not sure here but isn't instrumentation the component for all the plugin topics? Or would this result in some weird circular dependency?

[dyladan]

Not sure here but isn't instrumentation the component for all the plugin topics? Or would this result in some weird circular dependency?

Right now we have 2 ways to write instrumentations. The old way with "plugins" that use the BasePlugin class in the core module, and the new way which uses the Instrumentation base class in the instrumentation package. The old way will be deprecated when we finish migrating our existing instrumentations to the new way. The old plugin config interface was in the API package for some reason and this just moves it to core to live with the BasePlugin