Pin plugins to specific commits

[nrobinaubertin]

Overview

• avoid surprise updates from transient dependencies or plugins
• add the data-explorer plugin
• upgrading nodejs version (because the old one failed to download)

This is accomplished by pinning all the plugins to a specific commit and forcing the bundler to respect the Gemfile.lock file without updating the gems.
The specific commit for each plugin was chosen according to the discourse-compatibility specification.

⚠️ This also disables the self-hosted github runners usage that are being flaky lately.

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, complex)

[mthaddon]

LGTM, thx

[github-actions]

Test coverage for 6607a9d

Name              Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------
src/charm.py        303     34     86     17    87%   127, 129, 138, 140, 148-149, 289->294, 456, 468-470, 475, 486-488, 493, 505-507, 512, 524-526, 543-545, 585->exit, 592-593, 595->exit, 601, 629-635, 661->exit, 675-676, 686->exit, 700
src/database.py      30      1      8      1    95%   56
-------------------------------------------------------------
TOTAL               333     35     94     18    88%

Static code analysis report

Run started:2023-10-24 16:54:23.955886

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1818
  Total lines skipped (#nosec): 1
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):

[gtrkiller]

LGTM

[amandahla]

LGTM