fix: change public role like gamma procedure

[dpgaspar]

SUMMARY

Fixes #9807, by merging the Public role definition with pre-existing data access permissions (all other permissions not included on the template role are removed).

This PR also makes the definition of the Public role more configurable, for this PUBLIC_ROLE_LIKE_GAMMA is removed (breaking change) and a new key is introduced PUBLIC_ROLE_LIKE where a specific role can be set, like Admin, Alpha, Gamma or any other role preexisting on the DB or configured has a builtin role on the config itself.

To retain the same behaviour configure it the following way:

PUBLIC_ROLE_LIKE = "Gamma"

ADDITIONAL INFORMATION

• Has associated issue: Problems with Public role after updating #9807
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[villebro]

LGTM 🎉 One small convenience suggestion, although I'm not sure if we should be cluttering the codebase with these deprecation warnings, as UPDATING.md should be read by everyone anyway before updating.

[villebro]

To be super accomodating, we could do something like

if conf.get("PUBLIC_ROLE_LIKE_GAMMA", False):
    logger.warning("The config `PUBLIC_ROLE_LIKE_GAMMA` is deprecated and will be removed in Superset 1.0. Please use `PUBLIC_ROLE_LIKE ` instead.")
    self.copy_role("Gamma", self.auth_role_public, merge=True)

[dpgaspar]

Good idea

[codecov-commenter]

Codecov Report

Merging #10674 into master will decrease coverage by 0.06%.
The diff coverage is 94.59%.

@@            Coverage Diff             @@
##           master   #10674      +/-   ##
==========================================
- Coverage   64.36%   64.30%   -0.07%     
==========================================
  Files         785      785              
  Lines       36981    37016      +35     
  Branches     3530     3530              
==========================================
  Hits        23803    23803              
- Misses      13070    13101      +31     
- Partials      108      112       +4     

Flag	Coverage Δ
#cypress	54.09% <ø> (-0.73%)	⬇️
#javascript	60.91% <ø> (ø)
#python	59.87% <94.59%> (+0.15%)	⬆️

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

Impacted Files	Coverage Δ
superset/security/manager.py	91.01% <94.28%> (+0.85%)	⬆️
superset/config.py	90.38% <100.00%> (+0.03%)	⬆️
superset/connectors/sqla/models.py	89.72% <100.00%> (+0.13%)	⬆️
...et-frontend/src/SqlLab/reducers/getInitialState.js	33.33% <0.00%> (-16.67%)	⬇️
superset-frontend/src/reduxUtils.ts	70.88% <0.00%> (-8.87%)	⬇️
...rontend/src/SqlLab/components/TabbedSqlEditors.jsx	76.62% <0.00%> (-5.85%)	⬇️
superset-frontend/src/SqlLab/actions/sqlLab.js	60.25% <0.00%> (-4.28%)	⬇️
...rontend/src/SqlLab/components/SqlEditorLeftBar.jsx	44.00% <0.00%> (-4.00%)	⬇️
superset-frontend/src/SqlLab/reducers/sqlLab.js	37.75% <0.00%> (-3.32%)	⬇️
...end/src/SqlLab/components/TemplateParamsEditor.jsx	88.57% <0.00%> (-2.86%)	⬇️
... and 12 more

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[dpgaspar]

Added a very simple landing page for the public/anonymous users, since rendering the login page is not correct if the Public role is "activated".
I think this is enough to establish a working workflow for the anonymous users, we can iterate on more pretty landing page on a following PR.