Introduce PGVERSION

[sdudoladov]

Spilo doc:

PGVERSION: Specifies the version of postgreSQL to reference in the bin_dir variable (/usr/lib/postgresql/PGVERSION/bin) if postgresql.bin_dir wasn't set in SPILO_CONFIGURATION

Using PGVERSION is now preferred to setting postgresql.bin_dir in SPILO_CONFIGURATION

This changes works just fine with any recent Spilo. Anyway as a precaution, we provide the toggle pgversion_env_var
When it is "true", the environment contains only PGVERSION

postgres@acid-minimal-cluster-0:~$ echo $SPILO_CONFIGURATION
{"postgresql":{},"bootstrap":{"initdb":[{"auth-host":"md5"},{"auth-local":"trust"}],"users":{"zalandos":{"password":"","options":["CREATEDB","NOLOGIN"]}},"dcs":{}}}
postgres@acid-minimal-cluster-0:~$ echo $PGVERSION
12

Otherwise SPILO_CONFIGURATION contains the postgresql.bin_dir subsection and PGVERSION is unset. The latter behavior is not strictly necessary because in Spilo the bin_dir takes precedence over PGVERSION when both are set. I deliberately made this case more explicit on the operator side and decided not to set PGVERSION when bin_dir is provided.

Flipping pgversion_env_var costs a rolling upgrade because pod environment changes.

per request from @CyberDem0n

See Spilo PR 222 for details.
blocked by #1160
closes #554

[Jan-M]

So this PR will also remove bin dir from spilo configuration?

[sdudoladov]

So this PR will also remove bin dir from spilo configuration?

yes, it will.

[Jan-M]

👍

[sdudoladov]

👍