feat: add description column to Tags

[hughhhh]

SUMMARY

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

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

[codecov]

Codecov Report

Merging #24553 (33f812e) into master (38df1a8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 33f812e differs from pull request most recent head b148e1c. Consider uploading reports for the commit b148e1c to get more accurate results

@@           Coverage Diff           @@
##           master   #24553   +/-   ##
=======================================
  Coverage   69.08%   69.08%           
=======================================
  Files        1906     1906           
  Lines       74114    74115    +1     
  Branches     8155     8155           
=======================================
+ Hits        51200    51201    +1     
  Misses      20795    20795           
  Partials     2119     2119           

Flag	Coverage Δ
hive	53.92% <100.00%> (+<0.01%)	⬆️
mysql	79.40% <100.00%> (+<0.01%)	⬆️
postgres	79.48% <100.00%> (+<0.01%)	⬆️
presto	53.82% <100.00%> (+<0.01%)	⬆️
python	83.48% <100.00%> (+<0.01%)	⬆️
sqlite	78.04% <100.00%> (+<0.01%)	⬆️
unit	54.69% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
superset/tags/models.py	93.54% <100.00%> (+0.05%)	⬆️

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