[stable10] allow users to opt-out autocomplete in share dialog

[karakayasemi]

Backport of #34862

Description

allow users to opt-out autocomplete in sharing dialog

Also, I made some changes to simplify adding a new config option to personal sharing panel.

Related Issue

https://github.com/owncloud/enterprise/issues/3142

Motivation and Context

some users do not want to be found via autocomplete

How Has This Been Tested?

Manually tested by applying the following steps:

• Create a user test
• Login with admin
• Enable Allow username autocompletion in share dialog checkbox within the sharing admin panel
• Login with test
• Disable Allow finding you via autocomplete in share dialog from personal sharing panel with test user
• As an admin, search tes keyword in share dialog, test should not be listed
• Enable Allow finding you via autocomplete in share dialog from personal sharing panel with test user
• As an admin, search tes keyword in share dialog, test should be listed

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Database schema changes (next release will require increase of minor version instead of patch)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised: