[service]: add new subcommand to examine the initial configuration

[VihasMakwana]

Description

Why is this useful?

• Users might want to examine the config if they face any errors at boot time. This subcommand prints the configuration on stdout after merging and resolving from all the --config sources.
• The command prints the configuration even if it's invalid. This can help user to track down the faulty piece of config.

Usage

./otelcorecol examine --config=file:file.yaml --config=http://remote:8080/config --config=file:file2.yaml

Link to tracking issue

Fixes ##11479

Testing

Added unit test cases.

Documentation

Updated readme.

[codecov]

Codecov Report

Attention: Patch coverage is 90.32258% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.38%. Comparing base (44b3eed) to head (52e1abf).

Files with missing lines	Patch %	Lines
otelcol/command_print.go	90.00%	2 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (90.32%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11775      +/-   ##
==========================================
- Coverage   91.38%   91.38%   -0.01%     
==========================================
  Files         468      469       +1     
  Lines       25610    25641      +31     
==========================================
+ Hits        23404    23432      +28     
- Misses       1790     1792       +2     
- Partials      416      417       +1     

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[VihasMakwana]

@dmitryax @mauri870 can you take a look?

[mauri870]

Can you change to fmt.Printf here? This output is likely to be piped/redirected and I would rather not have a random timestamp at the start of the output.

[mauri870]

Reviewed again, LGTM. Thanks for adding a test to check the tool output.

[VihasMakwana]

@mx-psi I've addressed the review comments and added a feature flag for this new command. Please take a look!

Feature gate added

[VihasMakwana]

@mx-psi Thank you for your review. Once the CI is green, this should be good to go.

[mx-psi]

One thing left to address (not necessarily on this PR) is sensitive values. This would leak any sensitive values, so we need to make sure the user understands this