Allow search by workspace name and project name

[sklencar]

Not working search functionality for exploring project due to list project query has been changed. Note that shared and owned project are filtered locally in project's model, so only project to explore are filtered by a request.

Input used to have q as query parameter for listing project with search expression. It has been replaced for 3 separate flags for filtering either according namespace, name or last_updated.

#1048 changes search functionality to use name for time being.

[tomasMizera]

UPDATE: project list has been changed completely, however we still need an option on Mergin to search by namespace and name in the same parameter.