[mppi] add publish_critic_stats parameter for debug

[Alessio-Parmeggiani]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	-
Primary OS tested on	Ubuntu
Robotic platform tested on	Custom simulation
Does this PR contain AI generated software?	No
Was this PR description generated by AI software?	No

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Description of contribution in a few bullet points

This PR backports #5485 to humble_main branch.
It allow to publish statistics about each MPPI critic's cost contributions in a /critic_stats topic featuring a new message type: nav2_msgs/CritiicStats

Description of documentation updates required from your changes

Changed the nav2_mppi_controller readme to describe the new feature. Changes were copied from #5485.

Description of how this change was tested

I tested with different critics (also custom ones) if the topic was behaving correctly: I verified that it publishes coherent data, respecting score magnitude and disabled critics.

I wrote a simple program to visualize the data in a plot to validate the changes. This is a test output.

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists
• Should this be backported to current distributions? If so, tag with backport-*.

[mergify]

@Alessio-Parmeggiani, all pull requests must be targeted towards the main development branch.
Once merged into main, it is possible to backport to @humble_main, but it must be in main
to have these changes reflected into new distributions.

[mini-1235]

LGTM