Allow 'OR' for tags AND keywords in searches

Hi,

there are several other open issues in regards to the search but - imho - none of them describes this issue. Let me know if this is something already suggested.

**How to reproduce**
1. Search for a keyword which doesn't find anything.
2. Don't remove the keyword from the search and add a tag.
3. No result will be shown.
4. Remove the keyword and results for the tag will be shown.

**I expected** to see the result of the search including the keyword (0 results) and the tag (several results).

As it was explained to me, **the reason** for this:
So the way the Keywork + Tags search work is what we call in programming an AND combination. I.e. the results listed will have both the Keyword plus the Tag which the user has selected. What you are looking for is an OR search result. i.e the results should list Jobs containing any one of the Keyword or the Tag

Since there is already an option in the backend for the tags - just include the keywords a user might search for in this option or duplicate this option + add the keywords to allow more specific customization for end users. -> https://prnt.sc/n4j66c

**The reason, why I'd like to see this added:** A mutual user won't remove the keyword from the search. The user will see: "Oh, no results. Ok, so let's try the job tags provided." Unfortunately, since no results are shown (even if the job tags would provide jobs), the user will leave the website having the impression of "currently no jobs are available at all".

Thank you.

Start by reproducing the four search steps described in the issue and inspect the existing backend option for tag searches linked in the report. Done means a search combining a zero-result keyword with a tag returns the tag matches, while preserving the keyword-only behavior.

Written by the indexing model from the issue text.