[PLAY-871] MultiSelect Rails (#2590)

**What does this PR do?** 
This helps the rails multi_level_select correctly submit with forms.


**How to test?** Steps to confirm the desired behavior:
1. Go to /multi_level_select/rails
2. Scroll to the 3rd example
3. Test form submission (ignore after URL - this will be set by the
client)
4. Click on the network tab, to find the data submitted correctly! 🎉 

#### Checklist:
- [x] **LABELS** Add a label: `enhancement`, `bug`, `improvement`, `new
kit`, `deprecated`, or `breaking`. See [Changelog &
Labels](https://github.com/powerhome/playbook/wiki/Changelog-&-Labels)
for details.
- [x] **DEPLOY** I have added the `milano` label to show I'm ready for a
review.
- [x] **TESTS** I have added test coverage to my code.

---------

Co-authored-by: nida.ghuman <[email protected]>

playbook-website/Gemfile

@@ -22,6 +22,7 @@ gem "rouge", "~> 3.15"
 gem "faker"
 gem "will_paginate"
 
+
 group :development, :test do
   # Call 'byebug' anywhere in the code to stop execution and get a debugger console
   gem "byebug", platforms: %i[mri mingw x64_mingw]