Plugin tray open on show

[javerbukh]

Description

This pull request sets the plugin tray to be open by default when the application is shown.

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

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 milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone. Bugfix milestone also needs an accompanying backport label.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[pllim]

I cannot decide if we need a change log or not. The behavior change is very obvious and people might wonder if it is intentional.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.69%. Comparing base (930125f) to head (4ad336f).
Report is 175 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2892   +/-   ##
=======================================
  Coverage   88.68%   88.69%           
=======================================
  Files         109      109           
  Lines       16999    17047   +48     
=======================================
+ Hits        15076    15120   +44     
- Misses       1923     1927    +4     

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[kecnry]

Changelog can't hurt (but otherwise can just be tagged to not require the changelog so CI passes). Other than that - the code change probably isn't terribly controversial 😜