[Testing:Forum] Part replace of test_forum_merge_threads

[IDzyre]

Please check if the PR fulfills these requirements:

What is the current behavior?

Selenium tests are flaky, so we are porting them to cypress.

What is the new behavior?

This is a basic forum test, which adds three different forum threads, comments to them, merges them into one, then deletes the resulting thread.

[codecov]

Codecov Report

Merging #9393 (536864d) into main (77f0006) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main    #9393   +/-   ##
=========================================
  Coverage     23.31%   23.31%           
  Complexity     7972     7972           
=========================================
  Files           221      221           
  Lines         28386    28386           
  Branches         72       72           
=========================================
  Hits           6618     6618           
  Misses        21699    21699           
  Partials         69       69           

Flag	Coverage Δ
autograder	22.08% <ø> (ø)
js	28.01% <ø> (ø)
migrator	100.00% <ø> (ø)
php	20.29% <ø> (ø)
python_submitty_utils	71.65% <ø> (ø)
submitty_daemon_jobs	91.01% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[mahi-pas]

Should this be a draft?

[IDzyre]

I am working to refactor these tests to be more like the tests in profile.spec.js (instead of duplicating code, making functions to call instead)

[williamjallen]

This test seems reasonable to me, but I need to see the CI pass before I can approve. Please ping me or re-request a review when the tests are passing.