This patch removes code support for PG9.6 and PG10. In addition to
removing PG96 and PG10 macros the following changes are done:
remove HAVE_INT64_TIMESTAMP since this is always true on PG10+
remove PG_VERSION_SUPPORTS_MULTINODE
Previously the compile image for the ABI tests was based on a different
postgres image than the run image (e.g. 10-alpine vs 10.2-alpine). This
created dependency problems between different version of ssl packages
that may be available under different alpine versions.
We fix this by forcing the run image to be based off of the same image
as the compile version.
Test the ABI compatibility of postgres across minor version updates
wrt timescale. Namely, compile the extension on an early minor version
of postgres and test it on the latest snapshot of the major branch.
