feat: enable native JDBC connections

[olavloite]

Enables connections to PgAdapter from the native PostgreSQL JDBC driver. This requires a couple of minor tweaks to the startup protocol:

1. Some older versions of the JDBC driver require the encoding values to be in upper case (i.e. UTF8 instead of utf8).
2. The date style should also include the year-month-day order.
3. The value for standard_conforming_strings should be on or off (not true or false).

[Vizerai]

Overall LGTM. Maybe we should add in more pg-jdbc testing, but it doesn't have to be done in this PR.

[Vizerai]

Will this work with all other queries as well using pg-jdbc? I assume the wireprotocol is the same for pg-jdbc?

[olavloite]

Yes, the wireprotocol is the same for pg-jdbc, so yes it will in theory work with other queries. However:

1. The pg-jdbc driver uses binary format for many query parameter types, so we need to support that for parameterized queries to work. That is included in feat: add support incoming binary values #27
2. The pg-jdbc driver sends timestamp and date parameter values as untyped parameters. Support for that is also included in feat: add support incoming binary values #27 (only for timestamp at this moment, as we currently do not support date).
3. The pg-jdbc driver prefers the extended query mode over simple query mode (which is normally used in psql). That will probably also need some tweaking.

[olavloite]

Overall LGTM. Maybe we should add in more pg-jdbc testing, but it doesn't have to be done in this PR.

Yeah, I'll bring in a lot more test cases in separate PRs. #23 already contains a lot of test cases, but I decided to split it into several smaller PRs so it would be easier to review. Many of the test cases in #23 will only succeed once #27 has been merged, as the tests use parameterized queries and the pg-jdbc driver sends parameter values in binary format as opposed to the default text format used by psql.