mosviz gaussian smooth: only include data from spectrum-viewer

[kecnry]

Description

This pull request limits the data dropdown in the gaussian smooth plugin in mosviz to only include data entries in the (1d) spectrum-viewer.

Fixes #1451

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set?
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #1452 (132bf11) into main (050b62d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1452   +/-   ##
=======================================
  Coverage   85.16%   85.17%           
=======================================
  Files          91       91           
  Lines        8359     8362    +3     
=======================================
+ Hits         7119     7122    +3     
  Misses       1240     1240           

Impacted Files	Coverage Δ
...default/plugins/gaussian_smooth/gaussian_smooth.py	96.20% <100.00%> (+0.14%)	⬆️

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[pllim]

Works as advertised though now that I am looking at this plugin in Mosviz, I noticed something else that are out of scope but need new tickets for if there aren't already.

1. The data dropdown has extra blank line; not sure why.

2. The smoothed spectrum does not appear. I cannot tell if because the smoothed data is to hard to see or the linking is wrong. If the latter, maybe it needs a fix similar to Fix plugin linking in mosviz #1450 that @javerbukh has for model fitting.

[rosteen]

Works for me, although I had some minor performance issues. Seems like they're also present in main though.