Cherry-Pick Adding slow down at target heading to RPP Controller (#5361)

[zeerekahmad]

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Description of contribution in a few bullet points

Cherry picked from #5361

• Adding slow down at target heading to RPP
• Update test_regulated_pp.cpp

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]

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

[SteveMacenski]

This does not compile 🙃