Mention in the settings the side effect of outgoing federated shares

[danxuliu]

Until #20132 is fixed* the checkbox should explicitly mention its unexpected side effect.

*Note that the steps to reproduce mention using the viewer; the viewer case was fixed in nextcloud/viewer#581, but the issue of not being able to access public shares using WebDAV when outgoing federated shares are disabled is still valid

The wording of the option is just a suggestion; feel free to improve it :-)

When/If this is merged the user manual should be updated to reflect the new text in the settings.

Should this be backported to stable19 and stable18?

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 33063: failure

mariadb10.4-php7.3

Show full log

There were 2 warnings:

1) Test\Files\ViewTest::testRenameFailDeleteTargetKeepSource
Trying to configure method "writeStream" which cannot be configured because it does not exist, has not been specified, is final, or is static

2) Test\Files\ViewTest::testCopyFailDeleteTargetKeepSource
Trying to configure method "writeStream" which cannot be configured because it does not exist, has not been specified, is final, or is static

--

There were 2 failures:

1) Test\Files\Cache\UpdaterLegacyTest::testWrite
Failed asserting that 3619 matches expected 3606.

/drone/src/tests/lib/Files/Cache/UpdaterLegacyTest.php:101

2) OCA\Files_Sharing\Tests\SharedMountTest::testPermissionMovedGroupShare with data set #17 ('folder', 1, 21)
Failed asserting that false is true.

/drone/src/apps/files_sharing/tests/SharedMountTest.php:367

[rullzer]

Fine by me