feat: new Slack dashboard

[betodealmeida]

SUMMARY

New dashboard from @srinify showing Slack community.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

Ran superset load-examples and tested the new dashboard.

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov-io]

Codecov Report

Merging #12415 (db8a10f) into master (6bee3a0) will decrease coverage by 2.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12415      +/-   ##
==========================================
- Coverage   66.33%   64.00%   -2.33%     
==========================================
  Files        1014      485     -529     
  Lines       49528    29899   -19629     
  Branches     5074        0    -5074     
==========================================
- Hits        32854    19138   -13716     
+ Misses      16538    10761    -5777     
+ Partials      136        0     -136     

Flag	Coverage Δ
cypress	?
javascript	?
python	64.00% <100.00%> (-0.22%)	⬇️

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

Impacted Files	Coverage Δ
superset/datasets/commands/importers/v1/utils.py	55.55% <100.00%> (ø)
superset/examples/birth_names.py	73.19% <0.00%> (-25.65%)	⬇️
superset/db_engine_specs/mysql.py	79.59% <0.00%> (-12.25%)	⬇️
superset/common/query_context.py	82.51% <0.00%> (-3.59%)	⬇️
superset/db_engine_specs/presto.py	81.38% <0.00%> (-1.95%)	⬇️
superset/extensions.py	93.15% <0.00%> (-1.37%)	⬇️
superset/sql_lab.py	79.43% <0.00%> (-0.94%)	⬇️
superset/connectors/sqla/models.py	90.58% <0.00%> (-0.92%)	⬇️
superset/models/core.py	88.04% <0.00%> (-0.82%)	⬇️
superset/views/core.py	74.92% <0.00%> (-0.46%)	⬇️
... and 533 more

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