Add singleton flags to factories and standardize attributes

[djaglowski]

This PR is an extension of #11344 that addresses #11814.

Major changes:

• Add a Metadata() method to receiver.Factory, exporter.Factory and connector.Factory (processor.Factory excluded intentionally as described in Loggers for shared components should not report signal type. #11814). These Metadata() methods return Metadata structs, which act similarly to consumer.Capabilities in that they are intended as a set of information which describes the components which the factory produces.
• Remodels each component's as a proper go.opentelemetry.io/otel/attribute.Set. This set is used as the ID in the graph, but also as the set of attributes that creates the logger. In the future, the set will be automatically used to describe other aspects of the collector's own telemetry.
• The logger fields are changed to match those described in the component telemetry RFC.

Minor changes:

• Unknown component types are detected earlier in the startup process. (When the graph is being assembled, rather than when the components of the graph are being instantiated.) This is necessary so that we can obtain the Metadata from the appropriate factory. There is a minor user facing change in that the error message is not wrapped in a "could not build" prefix. I moved the processors to this pattern as well in order to match the other components.

[djaglowski]

If desired, I believe I can split this PR into several smaller PRs. However, I wanted to put this version up in order to show the overall picture.

[codecov]

Codecov Report

Attention: Patch coverage is 98.64407% with 4 lines in your changes missing coverage. Please review.

Project coverage is 91.72%. Comparing base (7425fe8) to head (256d7c9).

Files with missing lines	Patch %	Lines
service/internal/graph/exporter.go	92.59%	2 Missing ⚠️
service/internal/graph/receiver.go	95.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12057      +/-   ##
==========================================
+ Coverage   91.67%   91.72%   +0.05%     
==========================================
  Files         455      456       +1     
  Lines       24010    24171     +161     
==========================================
+ Hits        22010    22171     +161     
  Misses       1629     1629              
  Partials      371      371              

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[djaglowski]

I discovered when adding tests that singleton connectors will introduce broader changes into the way we build the graph, since we're wrapping each instance as a specific type of consumer. I've not been able to get it working yet but either way, the additional complexity seems not worth for now. I believe there are some reasons why singleton connectors would be useful but I'm going to propose for now that singleton instances are supported only for receivers and exporters. In the future we can try to add singleton connectors.