Add Content Security Policy

[samuelwei]

Fixes #315

Type (Highlight the corresponding type)

• Bugfix
• Feature
• Documentation
• Refactoring (e.g. Style updates, Test implementation, etc.)
• Other (please describe):

Checklist

• Code updated to current develop branch head
• Passes CI checks
• Is a part of an issue
• Tests added for the bugfix or newly implemented feature, describe below why if not
• Changelog is updated
• Documentation of code and features exists

Changes

• Add Content Security Policy
• Add strict css allowlist filter for room description

[codecov]

Codecov Report

Attention: Patch coverage is 60.86957% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 95.63%. Comparing base (88b0662) to head (a0ea26f).

Files	Patch %	Lines
app/Support/CSPPolicy.php	57.14%	9 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #1090      +/-   ##
=============================================
- Coverage      95.82%   95.63%   -0.19%     
- Complexity      1248     1252       +4     
=============================================
  Files            191      193       +2     
  Lines           4259     4282      +23     
=============================================
+ Hits            4081     4095      +14     
- Misses           178      187       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.