Rebase to 3.21

[thespad]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

I'm on my nonsense again.

If anyone can figure our how to get the firstrun to work properly with RO please do. For some reason it tries to use /var/tmp instead of honouring TMPDIR like everything else.

Goes without saying this will need a bit of testing. Done what I can and didn't run into any serious problems, but I imagine if someone's really screwed with their custom.cnf it could have an impact.

Benefits of this PR and context:

How Has This Been Tested?

Source / References:

[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/mariadb/11.4.4-r1-pkg-81a873c5-dev-abf6e2c4dd3f738f8ddd0ceb5ace62bc550553c3-pr-159/index.html
https://ci-tests.linuxserver.io/lspipepr/mariadb/11.4.4-r1-pkg-81a873c5-dev-abf6e2c4dd3f738f8ddd0ceb5ace62bc550553c3-pr-159/shellcheck-result.xml

Tag	Passed
amd64-11.4.4-r1-pkg-81a873c5-dev-abf6e2c4dd3f738f8ddd0ceb5ace62bc550553c3-pr-159	✅
arm64v8-11.4.4-r1-pkg-81a873c5-dev-abf6e2c4dd3f738f8ddd0ceb5ace62bc550553c3-pr-159	❌

[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/mariadb/11.4.4-r1-pkg-0be52e3f-dev-df0c7d93333c824cfe6851d9355e578fc23059c7-pr-159/index.html
https://ci-tests.linuxserver.io/lspipepr/mariadb/11.4.4-r1-pkg-0be52e3f-dev-df0c7d93333c824cfe6851d9355e578fc23059c7-pr-159/shellcheck-result.xml

Tag	Passed
amd64-11.4.4-r1-pkg-0be52e3f-dev-df0c7d93333c824cfe6851d9355e578fc23059c7-pr-159	✅
arm64v8-11.4.4-r1-pkg-0be52e3f-dev-df0c7d93333c824cfe6851d9355e578fc23059c7-pr-159	❌