fix: update regex to parse with whitespace

[joshtrichards]

For nextcloud/server#54822

Fixes the regex to handle whitespace (i.e. when our coding standards are applied to the config.sample.php ). Remains backwards compatible.

Also some refactoring (new comments, clearer variable names, etc.)

Tested existing config.sample.php as well as the one proposed in nextcloud/server#54822.

TODO:

• Once merged, update the Docker image that runs convert in production

[ChristophWurst]

Looks good when reviewed commit by commit

[joshtrichards]

@nickvergessen Can you bump a new docker-ci image for this? May already be doing so for #12 but just in case. Thanks!