first commit for mirroring age retention

[Rick-Methot-NOAA]

Concisely describe what has been changed/addressed in the pull request.

Implements a tested update of the mirroring of age-discard parameters

• Resolves issue [Bug]: mirroring was not working for age discard #676

What tests have been done?

Where are the relevant files?

files provided by @chantelwetzel-noaa

What tests/review still need to be done?

close examination of output by reviewer

Is there an input change for users to Stock Synthesis?

<-- - [x] No, there was no input change. -->

Additional information (optional).

[chantelwetzel-noaa]

I have confirmed that everything now appears to be working as expected. The initial r4ss github action failed for this pull request, but I have confirmed that I was able to use SS_output(), SS_plots(), and SSsummarize() on my installed r4ss version.

[iantaylor-NOAA]

I have confirmed that everything now appears to be working as expected. The initial r4ss github action failed for this pull request, but I have confirmed that I was able to use SS_output(), SS_plots(), and SSsummarize() on my installed r4ss version.

I'm guessing this was just a random error installing the r4ss package. I've just restarted the actions.

[e-perl-NOAA]

@iantaylor-NOAA It seems that even more ubuntu libraries need to be added to get r4ss working. Idk what they keep doing to the ubuntu runners that is requiring more and more libraries to need to be installed to get certain R packages to work.

[iantaylor-NOAA]

@iantaylor-NOAA It seems that even more ubuntu libraries need to be added to get r4ss working. Idk what they keep doing to the ubuntu runners that is requiring more and more libraries to need to be installed to get certain R packages to work.

Thank you @e-perl-NOAA!

[e-perl-NOAA]

I will leave the final approval up to @chantelwetzel-noaa but all actions are now passing.