Smgr extension API

[MMeent]

Introduce an SMGR API to PostgreSQL that Neon could plug into.

Anastasia started a thread on that here:

https://www.postgresql.org/message-id/CAP4vRV6JKXyFfEOf%3Dn%2Bv5RGsZywAQ3CTM8ESWvgq%2BS87Tmgx_g%40mail.gmail.com

New Redux thread^1 in commitfest^2

[andreasscherbaum]

Tristan: Apparently Percona is using it in one of their extensions

https://github.com/Percona-Lab/pg_tde/

Let's talk to Percona about reviews.

[andreasscherbaum]

Contacted Percona and asked for joint work on this.

[x4m]

Yezzey (our version of compute-storage separation for Greenplum) also works on an older variant of this. If you wish we can review the patch, but it's WoA now.

[andreasscherbaum]

Percona agreed to work together on this.

[andreasscherbaum]

Mail is sent to Percona.