feat: LEAP-2012: Add official docs remaining plugins to the repo

[nass600]

Description

Added 2 new plugins based on the docs:

• https://docs.humansignal.com/guide/plugin_examples#Sync-videos-with-frame-offset
• https://docs.humansignal.com/guide/plugin_examples#Custom-validation

Merged docs plugin with a existing one:

• https://docs.humansignal.com/guide/plugin_examples#Bulk-creation-and-deletion-operations-with-keyboard-shortcut

Related Issues

Fixed a bug with pausing annotator restoring the reason to pause to CUSTOM_SCRIPT

Checklist

• I have tested the changes in the Label Studio Labeling Config.
• I have added the plugin.js file.
• I have added the view.xml file.
• My code follows the guidelines stated in the README.md.

[hlomzik]

Good additions to our plugin gallery!
There are some questions and suggestions to make code better and cleaner.
Also would be great to use better approach to Bulk labeling from the script we already have, but it's okay to do it later in a separate PR (reference)

[yyassi-heartex]

looks good, though minor nitpick - we should have biome rules apply here - so our codebases coding styles are consistent - one thing that I found distracting while reviewing this PR was the 4 spaces per tab but thats a non-blocker for purposes of this ticket

[hlomzik]

oh, all these files have tabs instead of spaces... yeah, we should definitely apply proper linting rules here.