chore: deprecate /superset/add_slices

[dpgaspar]

SUMMARY

Found no references on superset-frontend for this old endpoint. Theres no exact replacement but the same can be achieved by calling /api/v1/chart/<id> PUT and adding the chart to a dashboard (no bulk update)

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 #23936 (f4ab69f) into master (93789b8) will not change coverage.
The diff coverage is 100.00%.

❗ Current head f4ab69f differs from pull request most recent head b38482d. Consider uploading reports for the commit b38482d to get more accurate results

@@           Coverage Diff           @@
##           master   #23936   +/-   ##
=======================================
  Coverage   68.18%   68.18%           
=======================================
  Files        1941     1941           
  Lines       75241    75241           
  Branches     8158     8158           
=======================================
  Hits        51306    51306           
  Misses      21852    21852           
  Partials     2083     2083           

Flag	Coverage Δ
hive	53.17% <100.00%> (ø)
mysql	78.90% <100.00%> (ø)
postgres	78.97% <100.00%> (ø)
presto	53.09% <100.00%> (ø)
python	82.75% <100.00%> (ø)
sqlite	77.50% <100.00%> (ø)
unit	52.98% <100.00%> (ø)

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

Impacted Files	Coverage Δ
superset/views/core.py	75.35% <100.00%> (ø)

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[Antonio-RiveroMartnez]

LGTM!