[IMPROVEMENT] - add warning before submitting spoiler

[janssensjelle]

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply.

• Bugfix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality not to work as expected).
• Documentation Update (if none of the other choices applies).

Proposed changes

A feature request was made to add a warning message before being able to submit a spoiler. Recently people have been submitting malicious/fake links. Also changed the placeholder for the URL field so that the user is warned twice.

Checklist

Put an x in the boxes that apply.

• I have read and followed the CONTRIBUTING.md
  doc.
• Lint and unit tests pass locally with my changes.
• I have added the necessary documentation (if appropriate).

Additional context

After the /spoiler command is triggered, an ephermal message will show. Clicking the Proceed button will open the spoiler modal.

[dimoschi]

PR looks good, thank you for your contribution!

[codecov]

Codecov Report

Attention: Patch coverage is 44.44444% with 10 lines in your changes missing coverage. Please review.

Project coverage is 53.66%. Comparing base (3024606) to head (a232dbb).
Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cmds/core/other.py	44.44%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
- Coverage   53.72%   53.66%   -0.07%     
==========================================
  Files          44       44              
  Lines        2468     2482      +14     
==========================================
+ Hits         1326     1332       +6     
- Misses       1142     1150       +8     

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