Make individual terms in process properties searchable

[BartChris]

The long term concept for improving metadata search in Kitodo production is to use the metadata of a process (which seems to be already indexed) to search for a process by its metadata.

see: #3512

Right now the properties can be used for searching, but the current configuration of the search requires that the search query to exactly match the content of a property because it targets the keyword subfield of the property. It is therefor not possible to search e.g. for only a part of a title. There is also no normalization applied, so that the query must match exactly what's in the field. This makes the search not really useful in my opinion.

In order to give a little better search experience i propose to enable searching also for parts of a property, e.g. parts of a title, by removing the "keyword"-setting.

[oliver-stoehr]

This change looks good to me.
I observed one limitation: It is only possible to search for parts of a property that are individual words. For example, when searching for "test" it is possible to find "test one" and "test two", but not "testOne" or "testTwo".

In my opinion it might be a good extension of this feature to find all substrings like the before mentioned. But that should be part of a another, future development.