Extend TAP tests of pg_dump to test for compression with gzip

Extend TAP tests of pg_dump to test for compression with gzip

The test logic is extended with two new concepts:
- Addition of a compression command called compress_cmd, executed
between restore_cmd and dump_cmd to control the contents of the dumps.
In the case of this commit, this is used to compress or decompress
elements of a dump to test new code paths.
- Addition of a new flag called compile_option, to check if a set of
tests can be executed depending on the ./configure options used in a
given build.

The tests introduced here are for gzip, but they are designed so as they
can easily be extended for new compression methods.

Author: Georgios Kokolatos, Rachel Heaton
Discussion: https://postgr.es/m/faUNEOpts9vunEaLnmxmG-DldLSg_ql137OC3JYDmgrOMHm1RvvWY2IdBkv_CRxm5spCCb_OmKNk2T03TMm0fBEWveFF9wA1WizPuAgB7Ss=@protonmail.com