[DRAFT] [DO NOT MERGE] Entities support prototype

[dmitryax]

Updated version of tigrannajaryan#4

Additional changes:

• Resource now has additional slice fields to reference attributes for the entity that this resource represents.
• EntitiesData now includes a resource that represents a parent entity. It allows all entities in the EntitiesData message to have local identities in the context of the parent entity.

[codecov]

Codecov Report

Attention: Patch coverage is 84.19453% with 104 lines in your changes missing coverage. Please review.

Project coverage is 91.92%. Comparing base (4dbbb90) to head (e503672).

Files with missing lines	Patch %	Lines
pdata/pentity/entities.go	0.00%	24 Missing ⚠️
pdata/internal/wrapper_entities.go	0.00%	16 Missing ⚠️
receiver/receiver.go	0.00%	11 Missing ⚠️
consumer/entities.go	0.00%	9 Missing ⚠️
pdata/pentity/event_type.go	0.00%	9 Missing ⚠️
...rter/debugexporter/internal/otlptext/databuffer.go	27.27%	8 Missing ⚠️
exporter/exporter.go	27.27%	8 Missing ⚠️
processor/processor.go	27.27%	8 Missing ⚠️
cmd/mdatagen/internal/validate.go	33.33%	4 Missing and 2 partials ⚠️
pdata/pentity/generated_entityevent.go	93.22%	2 Missing and 2 partials ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11282      +/-   ##
==========================================
- Coverage   92.14%   91.92%   -0.22%     
==========================================
  Files         433      452      +19     
  Lines       20389    21044     +655     
==========================================
+ Hits        18787    19345     +558     
- Misses       1238     1331      +93     
- Partials      364      368       +4     

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