Fix different function signature for loadExtension function in docs and code

[m1mir]

Fixed the argument names for loadExtension usages in the code examples and rewritten the function bodies to use the new names.

Closes #19668

[carsonbot]

It looks like you unchecked the "Allow edits from maintainer" box. That is fine, but please note that if you have multiple commits, you'll need to squash your commits into one before this can be merged. Or, you can check the "Allow edits from maintainers" box and the maintainer can squash for you.

Cheers!

Carsonbot

[m1mir]

I'm aware that CI is failing but, because the intended change and predefined rules are in conflict, I'd like to ask for maintainer input. The reasons for this are the following:

• The changing or deleting of the rule to accept the changes in this PR would mean that half of the argument_variable_must_match_type rules would be modified in a PR that didn't originally intend to do so.
• Changing the accepted name would affect the examples of the ExtensionInterface::load function, where the argument name is actually container on the interface.

[OskarStark]

Cc @alamirault

[m1mir]

Fixed in the new code snippet in #19793.