Allow using org-ql-select with string queries

### OS/platform

Any

### Emacs version and provenance

No dependency on emacs version I guess

### Org version and provenance

No dependency on org version as well

### org-ql package version and provenance

0.9-pre melpa

### Description

As discussed on reddit, it would be nice to have a way to use `org-ql-select` with string queries. I see two ways for that:

* either support string queries in `org-ql-select explicitly`
* or make `org-ql--query-string-to-sexp` a public function, so that the user could build sexp query from string by themselves

(or maybe both)

### Etc.

_No response_