feat: use allow_alter_system on Postgres >=17

[armru]

Closes #4244

[github-actions]

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[leonardoce]

E2e tests: https://github.com/EnterpriseDB/cloudnative-pg/actions/runs/9613127847

[mnencia]

/ok-to-merge E2E tests green

[gbartolini]

Tested it with this cluster definition:

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: clapton
spec:
  imageName: ghcr.io/cloudnative-pg/postgresql:17beta1-bookworm
  instances: 3
  postgresql:
    enableAlterSystem: false

then ran:

kubectl exec -ti clapton-1 -c postgres -- psql -c 'show allow_alter_system'
 allow_alter_system
--------------------
 off
(1 row)

And:

kubectl exec -ti clapton-1 -c postgres -- psql -c 'alter system set max_connections to 200;'
ERROR:  ALTER SYSTEM is not allowed in this environment

I then applied this:

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: clapton
spec:
  imageName: ghcr.io/cloudnative-pg/postgresql:17beta1-bookworm
  instances: 3
  postgresql:
    enableAlterSystem: true

then ran:

kubectl exec -ti clapton-1 -c postgres -- psql -c 'show allow_alter_system'
 allow_alter_system
--------------------
 on
(1 row)

The log reported:

{
  "level": "info",
  "ts": "2024-06-29T18:18:24Z",
  "logger": "postgres",
  "msg": "record",
  "logging_pod": "clapton-1",
  "record": {
    "log_time": "2024-06-29 18:18:24.876 UTC",
    "process_id": "28",
    "session_id": "66804ec0.1c",
    "session_line_num": "14",
    "session_start_time": "2024-06-29 18:13:20 UTC",
    "transaction_id": "0",
    "error_severity": "LOG",
    "sql_state_code": "00000",
    "message": "parameter \"allow_alter_system\" changed to \"on\"",
    "backend_type": "postmaster",
    "query_id": "0"
  }
}

I then checked that the postgresql.auto.conf file is not read only:

kubectl exec -ti clapton-1 -c postgres -- bash

Then inside I ran:

postgres@clapton-1:~/data/pgdata$ ls -la $PGDATA/postgresql.auto.conf
-rw------- 1 postgres tape 88 Jun 29 18:13 /var/lib/postgresql/data/pgdata/postgresql.auto.conf

Version 17 works.