fix: no roles being returned for anonymous user

[aspedrosa]

SUMMARY

Since 1.2.0 an anonymous user is unable to see a public dashboard.
This is caused because:

1. no roles are attached to an anonymous user
2. on the bootstrap_user_data function, when the user is anonymous, the permissions fetching process is skipped.

This will lead to an empty user payload

leading to an Unexpected error on the dashboard page.

My changes: since an anonymous user doesn't have roles associated, on the bootstrap_user_data function, I associate the public role to it, which then on this line respective permissions can be fetched.

BEFORE/AFTER

Before:
Screenshots present on the three issues descriptions

After:
Dashboards are displayed without login

TESTING INSTRUCTIONS

1. Add the permission mentioned in this comment to the public role OR set PUBLIC_ROLE_LIKE = "Gamma"
2. Create a dashboard if don't have any
3. Copy the URL for the dashboard
4. Logout or enter an anonymous browser session
5. Enter in the dashboard's URL
6. Check if it renders properly with no Unexpected error.

ADDITIONAL INFORMATION

• Has associated issue: unable to see public dashboards in Firefox anonymous session #14912, Public access to dashboard not working in 1.2.0rc2 #15280, Superset dashboard fails to load for anonymous user #14504
• 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 #15585 (9f20996) into master (86a59a2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 9f20996 differs from pull request most recent head 244cad5. Consider uploading reports for the commit 244cad5 to get more accurate results

@@           Coverage Diff           @@
##           master   #15585   +/-   ##
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  Coverage   76.87%   76.87%           
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  Files         976      976           
  Lines       51292    51293    +1     
  Branches     6907     6907           
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+ Hits        39430    39431    +1     
  Misses      11643    11643           
  Partials      219      219           

Flag	Coverage Δ
hive	81.28% <100.00%> (+<0.01%)	⬆️
mysql	81.54% <100.00%> (+<0.01%)	⬆️
postgres	81.57% <100.00%> (+<0.01%)	⬆️
python	81.94% <100.00%> (+<0.01%)	⬆️
sqlite	81.18% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
superset/views/utils.py	83.33% <100.00%> (+0.06%)	⬆️

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[aspedrosa]

@suddjian

[suddjian]

Thanks for the fix!

[geido]

LGTM! It looks like unit tests require some attention. Thanks!

[aspedrosa]

I have seen other commits on master also failing the test that failed on this PR. Maybe it is not related.
For example, the tests of the associated PR for this commit passed, however, the tests for the merge commit failed