Document the Search page (Advanced queries and Filters)

[zubeydecivelek]

https://github.com/CERNDocumentServer/docs-cds-rdm/blob/main/docs/search/search.md

Add documentation that explains:

• Advanced queries: Supported query syntax, field-specific search, and examples.
• Filters: Available filters (e.g. resource type, publication date, access status) and how to use them in the UI.
• Move search content from https://repository.cern/help/search to https://repository.cern/docs/search/search/

[kpsherva]

this issue does not have attached PR?