fix: add dashboard markdown id

[krsnik93]

SUMMARY

This PR adds html id's to dashboard markdown components. Fixes #15358. Added so that different css can be applied to each markdown, which I was not able to do previously.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before screenshots can be seen in #15358.

After screenshots:

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue: Add html id to markdown components #15358
• 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

[codecov]

Codecov Report

Merging #15418 (9f4fe6a) into master (f53b2c6) will decrease coverage by 0.22%.
The diff coverage is n/a.

❗ Current head 9f4fe6a differs from pull request most recent head 4d38b5f. Consider uploading reports for the commit 4d38b5f to get more accurate results

@@            Coverage Diff             @@
##           master   #15418      +/-   ##
==========================================
- Coverage   77.22%   76.99%   -0.23%     
==========================================
  Files         975      975              
  Lines       50634    50634              
  Branches     6222     6222              
==========================================
- Hits        39104    38988     -116     
- Misses      11319    11435     +116     
  Partials      211      211              

Flag	Coverage Δ
hive	?
javascript	71.75% <ø> (ø)
presto	?

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

Impacted Files	Coverage Δ
...c/dashboard/components/gridComponents/Markdown.jsx	82.82% <ø> (ø)
superset/config.py	91.15% <ø> (ø)
superset/db_engines/hive.py	0.00% <0.00%> (-82.15%)	⬇️
superset/db_engine_specs/hive.py	69.20% <0.00%> (-17.21%)	⬇️
superset/db_engine_specs/presto.py	83.36% <0.00%> (-6.53%)	⬇️
superset/views/database/mixins.py	81.03% <0.00%> (-1.73%)	⬇️
superset/connectors/sqla/models.py	88.22% <0.00%> (-1.65%)	⬇️
superset/db_engine_specs/base.py	87.97% <0.00%> (-0.41%)	⬇️
superset/models/core.py	89.76% <0.00%> (-0.27%)	⬇️
superset/utils/core.py	88.97% <0.00%> (-0.13%)	⬇️

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[krsnik93]

@suddjian I made a small change - decided to drop the redundant dashboard-markdown- prefix after reading up on the way IDs are created. Sorry about that.