[AMCL] pf_z's default value seems wrong and is assigned directly into pop_z

[Mygao]

https://github.com/ros-planning/navigation2/blob/db974ea91b1eb01d7abf094aad511c0f2306d55f/nav2_amcl/src/amcl_node.cpp#L160

Above, pf_z value is set to 0.99 and this is likely set with probability in mind.

Eventually pf_z value goes to pop_z value in pf.c and regarding the paper this value is quantile value: for 99% probability, appropriate value should be around 3(this is set right in pf_alloc function: pop_err as 0.01 and pop_z as 3).

I think default value should be 3.

[SteveMacenski]

I yield to @mikeferguson on this one since I know it’s more topical for him, but in general I’m not in love with changing defaults inline in the code after all these years. Changing defaults in our provided configurations in nav2 bringup and the documentation is definitely possible though!

If he says you’re right and it’s a better global value, we can update it in the code. If he thinks it’s right but not objectively a better global value, we can update it in the docs and bringup so folks can leverage it.