Decode Content Clean-up

[timolegros]

Link to Issue

Closes: #9184

Description of Changes

• Removed plaintext and body_backup columns

"How We Fixed It"

Test Plan

1. Create threads with a variety of formats (using markdown) and ensure the thread previews appear normal
   Important: Ensure Thread preview on mobile appears broken #8611 is not reintroduced.
   Context:

     // Future Ref: this fixes https://github.com/hicommonwealth/commonwealth/issues/8611 for iOS mobile
     // where quill renders broken/cut-off/overlapping thread.plaintext in cases when there are multiple
     // <p/> tags in the quill delta for thread.plaintext or if thread.plaintext has \n characters which
     // iOS devices don't seem to render correctly.
   

   I replaced thread.plaintext.replaceAll(/\n/g, '').slice(0, 150) with thread.body which is raw markdown that may contain /n.

2. Using the previously created thread, create a snapshot proposal. Images should be removed but all markdown should be properly rendered.

Deployment Plan

Other Considerations

[timolegros]

This PR is technically ready (minus any conflicts) but cannot be merged until the decoding scripts from #9183 are executed in production. Will leave this PR in draft until then.

[timolegros]

@mzparacha tagging you here for review to ensure we don't regress on #8611

[mzparacha]

@mzparacha tagging you here for review to ensure we don't regress on #8611

sry I missed this, will review early tomorrow

[mzparacha]

Tested #8611 and it works well for me on iOS safari. Would like @masvelio to take a look as well.

1. Found an unformattable markdown error using markdown from here (probably an editor issue - not directly related to this PR cc: @burtonator)

2. Getting some raw quill deltas rendered in home feed

cc: @timolegros

[mzparacha]

Update: 2 from #9251 (comment) is resolved after running content decode scripts (TY @timolegros). I wasn't able to repro 1 from #9251 (comment) in the master branch + the markdown doesn't render there correctly cc: @burtonator

[mzparacha]

The markdown bug was with the new editor, everything works well. TY for all the changes