Change default image viewer percentile to 95%

[pllim]

Description

This pull request is to change the default percentile from min/max to 95% so typical astronomical images show better on load.

Fixes #577

Previous failed attempts:

• Change default percentile for Imviz #605
• Imviz: Set default percentile to 95 #710
• Change default percentile to 95 glue-viz/glue#2199

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 #1386 (e1a0278) into main (8c3d3e7) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1386   +/-   ##
=======================================
  Coverage   84.91%   84.91%           
=======================================
  Files          91       91           
  Lines        8288     8288           
=======================================
  Hits         7038     7038           
  Misses       1250     1250           

Impacted Files	Coverage Δ
jdaviz/app.py	92.75% <100.00%> (ø)

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[rosteen]

🌟

[kecnry]

Wow, such a simple solution!

[pllim]

I was surprised too. 😆 Thanks for the reviews!