Support search endpoint

[aleixq]

Once again as in #1 and #64 I think that search endpoint will be useful outside nextcloud. It uses this route:

/core/search provided by search controller
Otherwise is not possible to search from outside origin.

[aleixq]

As a note, while not exactly the same, webdav search feature is enabled when enabling webdav as usual with webapppassword, to show what it is doing look at my effort in providing a interface for searching in a filepicker with julien-nc/nextcloud-webdav-filepicker#9