refactor: Convert custom form template to bootstrap

[pselkirk]

Fixes #6411

[pselkirk]

This creates a small change in the UI - extra fields, slight reordering.

Before:

After:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ce918c4) 88.80% compared to head (fd438a3) 88.81%.
Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6763   +/-   ##
=======================================
  Coverage   88.80%   88.81%           
=======================================
  Files         285      285           
  Lines       40277    40285    +8     
=======================================
+ Hits        35769    35778    +9     
+ Misses       4508     4507    -1     

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[rjsparks]

What the form shows can be controlled now by https://github.com/ietf-tools/datatracker/pull/6763/files#diff-a2a76783d6a823963a5dfad1b48beba6e254c40a3d2d8f6a3944a50bfeb0fd81R364

@cindymorgan - do you care about the order? Do you want us to let bcc/reply-to show up, or suppress them as the current form does?

[jennifer-richards]

lgtm