Added support for MPPI Controller to adjust wz_std parameter based on linear speed

[vahapt]

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	#5274
Primary OS tested on	(Ubuntu 24.04 Arm64, Ubuntu 24.04 x64 )
Robotic platform tested on	(Gazebo Simulation, Physical Robot)
Does this PR contain AI generated software?	(No)

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Description of contribution in a few bullet points

Added feature enables dynamic modification of wz_std (angular deviation) based on linear velocity of the robot.

When a robot with high inertia (e.g. 500kg) is moving fast and if wz_std is above 0.3, oscillation behavior can be observed.
Lowering wz_std stabilizes the robot but then the maneuvers take more time.

Dynamically reducing wz_std as vx, vy increase (speed of the robot) solves both problems.
Suggested values to start with: wz_std = 0.3, wz_std_decay_to = 0.05, wz_std_decay_strength = 5.0

The following is used as the decay function
f(x) = (wz_std - wz_std_decay_to) * e^(-wz_std_decay_strength * v_linear) + wz_std_decay_to

Description of documentation updates required from your changes

2 new parameters are added to nav2_mppi_controller, README.md updated accordingly

advanced.wz_std_decay_strength
advanced.wz_std_decay_to

Description of how this change was tested

On both physical and simulated robots, changes deployed and parameters changed through live parameter update.
Robot behavior change and oscillation effects observed and confirmed.

It should be noted that tests are performed with a differential drive robot setup, thus holonomic behavior or potential anomalies with ackermann control are not tested yet.

Unit tests created to test new computeAdaptiveStds function

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Future work that may be required in bullet points

• Decay function might be enhanced based on the user feedback
• vx_std, vy_std parameters can also be converted to adaptive easily

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-*.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
...nav2_mppi_controller/models/optimizer_settings.hpp	100.00% <ø> (ø)
...ude/nav2_mppi_controller/tools/noise_generator.hpp	100.00% <ø> (ø)
nav2_mppi_controller/src/noise_generator.cpp	100.00% <100.00%> (ø)
nav2_mppi_controller/src/optimizer.cpp	98.19% <100.00%> (+0.01%)	⬆️

... and 2 files with indirect coverage changes

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