RSQL queries do not work with PostgreSQL

[floruschbaschan]

With #1047 it was already mentioned that RSQL queries for PostgreSQL are handling numbers not like strings. Currently the Hawkbit UI does work with PostgreSQL since it is using the repository layer directly instead of the Management API. But once a REST request sends the FIQL query field q parameter, internal server errors are thrown:

Caused by: org.postgresql.util.PSQLException: ERROR: function upper(bigint) does not exist
Hint: No function matches the given name and argument types. You might need to add explicit type casts.

It looks like the CriteriaBuilder of RSQLUtility tries to apply upper() and like() functions on numbers and not strings for PostgreSQL.

Steps to reproduce:

• run PostgreSQL database
• run Hawkbit with active profile postgresql
• send an Management API request e.g. http://localhost:8080/rest/v1/targetfilters?q=id==*