Move export plot plugin to last in the listing

[pllim]

Description

It just bothers me that it is not listed last because usually you export at the end of the workflow. 😆

With this patch (example below from Imviz):

Checklist for package maintainer(s)

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• 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? Milestone is only currently required for PRs related to Imviz MVP.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[kecnry]

Although we can do this for now, it will likely move higher in the list once we decide on an actual "policy" for plugin ordering. The immediate downside to moving it to the bottom now is that the sidebar currently has no ability to "scroll to" when opening a plugin from a viewer toolbar. Granted this same annoyance happens when its at the top and you have other plugins below opened, but now its more apparent from the default app state.

[pllim]

Patrick never even used this feature (he said he takes screenshots), so unlikely anyone going to notice and it will stop bothering me, so win-win?

[codecov]

Codecov Report

Merging #1160 (64cb5f3) into main (9d90130) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1160   +/-   ##
=======================================
  Coverage   76.10%   76.10%           
=======================================
  Files          87       87           
  Lines        6667     6667           
=======================================
  Hits         5074     5074           
  Misses       1593     1593           

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[pllim]

Thanks for the discussions and approvals!