Make sure to use the active default values for preamble and postamble in the help text,
and provide the current default values as the default in the add_argument().
The only exception is uccnc_post.py, where the real default value depend on the use of
--no-comments, and sending the default argument to add_argument() would change behaviour.
This change was inspired by the changes done to fix (#20792) in
d84d9c9bd1.
* CAM Multiline POSTAMBLE and PREAMBLE in old postprocessors
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* CAM: Fix preamble and postamble help text
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
