Toast compression method options

We have already pushed the configurable lz4 toast compression code[1].
In the custom compression thread, we were already having the patch to
support the compression method options[2].  But the design for the
base patches was heavily modified before commit but I never rebased
this patch based on the new design.  Now, I have rebased this patch so
that we don't lose track and we can work on this for v15.  This is
still a WIP patch.

For v15 I will work on improving the code and I will also work on
analyzing the usage of compression method options (compression
speed/ratio).

[1] https://www.postgresql.org/message-id/E1lNKw9-0008DT-1L%40gemulon.postgresql.org
[2] https://www.postgresql.org/message-id/CAFiTN-s7fno8pGwfK7jwSf7uNaVhPZ38C3LAcF%2B%3DWHu7jNvy7g%40mail.gmail.com

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com