Add system property to disable closing connections after broken connections

[mrotteveel]

As suggested in https://github.com/FirebirdSQL/firebird/issues/8739 by @EPluribusUnum, add a system property to disable forcibly closing connections that Jaybird considers invalid.

I will note that I consider this something for debugging purposes and/or workaround of issues/bugs, and not a supported "feature". Continued use of connections in such cases is not at all guaranteed, and may result in undefined behaviour. Further details to be fleshed out in a JDP.

This should be added to Jaybird 5 and Jaybird 6, and master (Jaybird 7).