Bash skip empty query param fix

Created by: ccouzens

Skip empty params when generating URLs

I have a route with many optional query parameters.
I observed that when they weren't specified, they were still included in
the routes, but without a value or the `&` character to separate them.

Running:
```bash
bash bash_keycloak/client.sh -v --oauth2-bearer "$access_token" --host "$api_host" --dry-run realmUsersGet realm=demo_realm2 email=foo+bar@baz.com username=foo
```

Would produce the route:
`http://localhost:8080/auth/admin/realms/demo_realm2/users?briefRepresentation=email=foo+bar@baz.comfirst=firstName=lastName=max=search=&username=foo`

After this change it produces the route:
`http://localhost:8080/auth/admin/realms/demo_realm2/users?email=foo+bar@baz.com&username=foo`

Note, I haven't written much bash, so I'm not yet used to its
conventions.

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Description of the PR

See above