Add psalm workflow

[come-nc]

Lots of OC\ usage, if they are not removable we should stub them.

This one seem like a valid concern:

ERROR: InvalidPropertyAssignmentValue - lib/Provider/FilesProvider.php:94:26 - $this->indexOptions with declared type 'OCP\FullTextSearch\Model\IIndexOptions' cannot be assigned type 'array<empty, empty>' (see https://psalm.dev/145)
61
    private $indexOptions = [];

The property is indeed passed to methods which only accepts an IIndexOptions instance.

[come-nc]

/rebase

[come-nc]

/rebase