Allow IPv6 addresses with brackets for pgsql

[muhme]

🚧 DRAFT as to be extended by unit tests and documentation

Summary of Changes

IPv6 addresses are used with square brackets for MySQL and MariaDB and allowing the configuration of a non-default port number for the IPv6 address. However, with PostgreSQL, square brackets around IPv6 addresses are not usable, and setting a port is not possible.

Since it was decided to have only a single host field without a separate port number field in Joomla Web Installer (see issue #43902), there is a need to use square brackets to distinguish between the IPv6 host address and a port number.

This PR removes the square brackets somewhere in the middle, after separating a possible port number, but before continuing with PostgreSQL:

• PostgreSQL can now use IPv6 addresses with square brackets, just like MariaDB and MySQL → simplifies/unifies documentation and joomla-cypress-36 implementation
• For the first time, it is possible to configure a port number together with an IPv6 address for PostgreSQL.
• The change is fully backward compatible. In the past, IPv6 addresses were accepted without square brackets, and this will continue to be supported in the future as well.

Testing Instructions

🚧 DRAFT For the moment together with and will be added to joomla-cypress-36

Documentation Changes Required

TODO

[muhme]

This PR has been replaced by the alternative #316