feat: allow more HTML tags in report description

[ktmud]

SUMMARY

Our users want to write multi-line descriptions for alerts & reports. This PR adds <br>, <p>, <div>, as well as HTML table related tags to the list of allowed tags.

Slack messages need to be handled differently. We'll address it in future PRs if necessary.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

Unit test

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[ktmud]

This is basically bleach.ALLOWED_TAGS + ["br", "p", "div"]. Enumerate all of them so you don't have to jump to the source code of bleach to see the full list.

[codecov]

Codecov Report

Merging #20908 (6ad00dc) into master (50d2e5a) will decrease coverage by 11.44%.
The diff coverage is 55.55%.

❗ Current head 6ad00dc differs from pull request most recent head 0c44dee. Consider uploading reports for the commit 0c44dee to get more accurate results

@@             Coverage Diff             @@
##           master   #20908       +/-   ##
===========================================
- Coverage   66.31%   54.86%   -11.45%     
===========================================
  Files        1758     1758               
  Lines       67008    67010        +2     
  Branches     7107     7107               
===========================================
- Hits        44437    36766     -7671     
- Misses      20749    28422     +7673     
  Partials     1822     1822               

Flag	Coverage Δ
hive	53.25% <44.44%> (+<0.01%)	⬆️
mysql	?
postgres	?
presto	53.15% <44.44%> (+<0.01%)	⬆️
python	57.90% <55.55%> (-23.65%)	⬇️
sqlite	?
unit	50.60% <55.55%> (+0.35%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/models/helpers.py	37.32% <20.00%> (-3.46%)	⬇️
superset/reports/notifications/email.py	77.14% <100.00%> (-22.86%)	⬇️
superset/utils/core.py	62.88% <100.00%> (-27.36%)	⬇️
superset/utils/dashboard_import_export.py	0.00% <0.00%> (-100.00%)	⬇️
superset/key_value/commands/update.py	0.00% <0.00%> (-88.89%)	⬇️
superset/key_value/commands/delete.py	0.00% <0.00%> (-85.30%)	⬇️
superset/key_value/commands/delete_expired.py	0.00% <0.00%> (-80.77%)	⬇️
superset/dashboards/commands/importers/v0.py	15.62% <0.00%> (-76.25%)	⬇️
superset/datasets/commands/update.py	25.30% <0.00%> (-68.68%)	⬇️
superset/datasets/commands/create.py	29.41% <0.00%> (-68.63%)	⬇️
... and 280 more

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[john-bodley]

@ktmud you'll have to remove this to get CI to pass.