Rename GQL_URN to DEEPLINKS_GQL_PATH, and GQL_SSL to DEEPLINKS_GQL_SSL across all repositories

URN is for books and standards. To use for for GQL path/url is just wrong.

https://stackoverflow.com/questions/57446486/name-of-the-portion-of-a-url-that-follows-the-scheme
https://stackoverflow.com/a/38204721/710069
https://www.rfc-editor.org/rfc/rfc3986#section-4.2


The closest idea is relative reference of URL, but it contains `//` which we don't use in GQL_URN env.

Other variations:
```
UriWithoutSchema
UrlWithoutSchema
AuthorityWithPath

SCHEMELESS_URL
```

And may be we should use even better way to do it: https://github.com/deep-foundation/hasura/issues/15 (this way may be optional)