Created a config.php option to disable local mounts for files_external

[grischdian]

Description

This is the new PR promised in #26887 - could not commit any new changes to the old one.

As in #26653 mentioned an option would be good to disable the 'local' option from files_external.
There is now a new Option for config.php called 'files_external_deny_local' which is set to false on default. Only if you set the option to true then the local Backend will not get registered.

Related Issue

#26653

Motivation and Context

If Sysadmin and oCadmin are not the same the Sysadmin may want to disable the local mount feature for security reasons.

How Has This Been Tested?

Compiled the actual master, installed php56 and apach24 on centos7 (Softwarecollection)
Tested without setting the option in config.php, tested with the option set to false and set to true.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[mention-bot]

@grischdian, thanks for your PR! By analyzing the history of the files in this pull request, we identified @Xenopathic @carlaschroder, @butonic and @PVince81 to be a potential reviewer.

[PVince81]

Tested, works 👍

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.