chore: migrate available_domains to api/v1

[zephyring]

SUMMARY

Migrate /available_domains/ to api/v1/available_domains/

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 #21173 (b821bc1) into master (1d3a805) will decrease coverage by 0.00%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master   #21173      +/-   ##
==========================================
- Coverage   66.45%   66.45%   -0.01%     
==========================================
  Files        1784     1786       +2     
  Lines       68142    68198      +56     
  Branches     7264     7264              
==========================================
+ Hits        45285    45320      +35     
- Misses      20989    21010      +21     
  Partials     1868     1868              

Flag	Coverage Δ
hive	53.05% <90.00%> (+0.04%)	⬆️
mysql	80.84% <96.66%> (-0.04%)	⬇️
postgres	80.89% <96.66%> (-0.04%)	⬇️
presto	52.95% <90.00%> (+0.04%)	⬆️
python	81.37% <96.66%> (-0.04%)	⬇️
sqlite	79.41% <96.66%> (-0.03%)	⬇️
unit	50.67% <90.00%> (+0.09%)	⬆️

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

Impacted Files	Coverage Δ
superset/views/core.py	75.54% <0.00%> (-0.06%)	⬇️
superset/available_domains/api.py	100.00% <100.00%> (ø)
superset/available_domains/schemas.py	100.00% <100.00%> (ø)
superset/initialization/__init__.py	91.75% <100.00%> (+0.05%)	⬆️
superset/tasks/cache.py	61.15% <0.00%> (-12.76%)	⬇️
superset/databases/schemas.py	98.23% <0.00%> (-0.37%)	⬇️
superset/db_engine_specs/base.py	88.21% <0.00%> (-0.22%)	⬇️
superset/config.py	91.58% <0.00%> (-0.03%)	⬇️
superset/db_engine_specs/shillelagh.py	100.00% <0.00%> (ø)
superset/models/core.py	88.88% <0.00%> (+0.13%)	⬆️
... and 3 more

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[geido]

LGTM with Daniel's comment