DOC: Use intersphinx in glue dev doc link

[pllim]

Description

This pull request is to use intersphinx to an important link for devs that @astrofrog mentioned this morning. Not sure how to make it easier to find though.

http://docs.glueviz.org/en/stable/customizing_guide/viewer.html

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

[codecov]

Codecov Report

Merging #1100 (15092b9) into main (c6ba6f5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1100   +/-   ##
=======================================
  Coverage   76.03%   76.03%           
=======================================
  Files          82       82           
  Lines        6284     6284           
=======================================
  Hits         4778     4778           
  Misses       1506     1506           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c6ba6f5...15092b9. Read the comment docs.

[kecnry]

somewhere is better than nowhere!