Fix user_show for ckan.auth.public_user_details

[markstuart]

Fixes #7838

Proposed fixes:

Allows _check_access to evaluate the ckan.auth.public_user_details config so that it can return the correct 403 response and not leak information about what users are in the system.

Features:

• includes tests covering changes
• includes updated documentation
• includes user-visible changes
• includes API changes
• includes bugfix for possible backport

Please [X] all the boxes above that apply

[markstuart]

typecheck failing test is fixed in #7862

[Zharktas]

PR is made against the wrong branch, should be done against master and cherry-picked from the to dev-v2.10

[pdelboca]

Hello @markstuart we are moving forward with the release of CKAN 2.11 and we would love to have this fix.

Could you re create the PR but targeting master instead? If you do not have time, let me know and I would create a new one. (I don't want to steal your contribution)

[markstuart]

@pdelboca here you go, hopefully that works as expected. I'm very stretched for time right now, so I'd appreciate it if you could cherry-pick back to dev-v2.10 as suggested by @Zharktas.

[pdelboca]

Thanks @markstuart ! We'll backport it during the release process.