Is your feature request related to a problem? Please describe.
I prefer cgdb for debugging, however I cannot use it easily from coredumpctl.
Even when I try a PATH/symlink/helper script trick to override gdb on PATH,
and indeed, I can see it's interface for a bit, it will subsequently terminate.
I have no idea about the reason, may be that curses-based environment
relies on some signals (something else?) that are blocked.

I think that enabling to use the same scheme with automatic cleanup and presumably
enforced secure approach in general with arbitrary command with the same interface
would be very convenient.

Describe the solution you'd like
Two parts:

• make sure that cgdb is fully usable under coredumpctl's wrapping
• allow one to specify alternative gdb command with environment variable,
  e.g. GDB (for a start, no need to provide the overriding mechanism
  on the command line)

Describe alternatives you've considered
Making the coredump materialized in the filesystem with a separate command
(less convenient, possibly also less secure when the path not selected wisely).