New subcommand for dumping configs

[VihasMakwana]

This is a sub-issue created from #5223.

Is your feature request related to a problem? Please describe.
It would make sense to have a command line option which logs the final configuration. It is particularly useful for users when a config is created from multiple providers and expanded recursively.

Describe the solution you'd like
This option can be provided as a subcommand (like validate subcommand). This new subcommand would be helpful for introspection the configuration.

• Why a new subcommand?
  • Users should be able to view the config for debugging purposes, even if that config is invalid.

Additional context
I've got couple of suggestions for subcommand's name:

• inspect
• probe
• examine

From #5223 (comment),

I propose following:

• Enhance the validate subcommand with the --dump-config option, which will display the configuration after it has been resolved/expanded/merged from different sources.
• Add another option as a follow-up PR, --dump-mode, which will show both the configuration after resolving/expanding and the configuration after applying default settings.

This issue caters the first requirement.
As suggested by @mx-psi here, we should take a different approach for second requirement i.e. a new extension which exposes config over http and which can watch for runtime config updates.

[mx-psi]

Assigned to you @VihasMakwana! I think we can make a PR directly and discuss the specifics there :)

[axw]

Can this be closed? I think merging #11775 was intended to, but the "Fixes" syntax in the description is slightly off.

[VihasMakwana]

Yes, this can be closed @axw. Thanks!