[stable20] Add migration for oc_share_external columns

[backportbot-nextcloud]

⚠️ This backport had conflicts and is incomplete ⚠️

backport of #24829

[rullzer]

@PVince81@juliushaertl can you check the conflict?

[juliusknorr]

Rebased and added the missing version bump for the files_sharing app.

[faily-bot]

🤖 beep boop beep 🤖

Here are the logs for the failed build:

Status of 1057: failure

mariadb10.1-php7.2

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 bash tests/drone-run-php-tests.sh || exit 0
=========================
= List of changed files =
=========================
apps/files_sharing/appinfo/info.xml
apps/files_sharing/composer/composer/autoload_classmap.php
apps/files_sharing/composer/composer/autoload_static.php
apps/files_sharing/lib/Migration/Version11300Date20201120141438.php
apps/files_sharing/lib/Migration/Version21000Date20201223143245.php
=========================
bash files are modified
+ NOCOVERAGE=true TEST_SELECTION=DB ./autotest.sh mariadb
Using PHP executable /usr/bin/php
Using database oc_autotest
Setup environment for mariadb testing on local storage ...
Waiting for MariaDB initialisation ...
...........................................................................................................................................................................................................................................................................................................
[ERROR] Waited 300 seconds, no respons

mysql8.0-php7.2

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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 was 1 failure:
1) Test\Files\ViewTest::testDeleteGhostFolder
Failed asserting that '5ff6d62200fa2' is not equal to '5ff6d62200fa2'.
/drone/src/tests/lib/Files/ViewTest.php:2618