[configoptional] Add support for setting an 'enabled' field under a feature gate

[mx-psi]

Description

Adds support for disabling or enabling optional fields through an enabled key under an alpha feature gate, configoptional.AddEnabledField. For example, the following configuration becomes valid:

receivers:
  otlp:
    protocols:
      grpc:
        enabled: true

exporters:
  nop:

service:
  pipelines:
    traces:
      receivers: [otlp]
      exporters: [nop]

and is equivalent to:

receivers:
  otlp:
    protocols:
      grpc:

exporters:
  nop:

service:
  pipelines:
    traces:
      receivers: [otlp]
      exporters: [nop]

Link to tracking issue

Fixes #13894
Updates #14021

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.65%. Comparing base (c480657) to head (8fab976).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13995      +/-   ##
==========================================
+ Coverage   91.63%   91.65%   +0.01%     
==========================================
  Files         656      656              
  Lines       42801    42813      +12     
==========================================
+ Hits        39221    39240      +19     
+ Misses       2760     2755       -5     
+ Partials      820      818       -2     

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[lahsivjar]

Nice! LGTM!

[jade-guiton-dd]

Looks mostly good to me, although I think we'll want community feedback from end user and component author perspectives. Additionally, while I'm ambivalent about enabled vs. disabled, others may have strong opinions.

[jmacd]

Nice!

[songy23]

👍

[mx-psi]

I am going to bring this PR up on the next spec meeting given the discussion on open-telemetry/opentelemetry-specification/issues/4344 has not been resolved yet and is relevant for this PR

[mx-psi]

I am going to bring this PR up on the next spec meeting given the discussion on open-telemetry/opentelemetry-specification/issues/4344 has not been resolved yet and is relevant for this PR

After spending some time earlier this week writing open-telemetry/opentelemetry-specification#4344 (comment) down and looking at the discussion I think we should go ahead with enabled.

We can revisit the discussion before the feature gate hits beta in case I manage to get some traction at the spec, but given the widespread usage of enabled in the Collector already, I don't feel like this PR makes it significantly worse.

[mx-psi]

I am going to merge this once I get Jade's approval so we can continue validating this. Since this is in alpha we can still change our minds along the way