allow for different postgres versions

[pb82]

Allow the script to work with different postgres versions. It will default to 9.6 if POSTGRES_VERSION is not set in the secret.

Verification steps:

1. Make sure backup is installed in your cluster
2. Delete the 3scale-postgres-backup cronjob in order to avoid confusion (not strictly required)
3. build an image from this branch and run:

oc new-app \
-f backup-job-template.yaml \
-p 'COMPONENT=postgres' \
-p 'COMPONENT_SECRET_NAME=threescale-postgres-secret' \
-p 'COMPONENT_SECRET_NAMESPACE=openshift-integreatly-backups' \
-p 'BACKEND_SECRET_NAME=s3-credentials' \
-p 'IMAGE=docker.io/pb82/backup-container-image:latest' \
-p 'NAME=3scale-postgres-backup' \
-p 'PRODUCT_NAME=3scale'

1. It should fail with the error that the pg_dump version does not match the database version. You can check the logs by getting the pods first and then using oc logs <backup job pod name>
2. Now edit the secret: oc edit secret threescale-postgres-secret
3. and add a POSTGRES_VERSION: MTAK to the data (MTAK is base64 for 10).
4. Delete the job and recreate it
5. Check the logs again. This time the pg dump should work. The job will likely still fail because the encryption secret is missing or invalid. But the important part is that the database dump works.

[odra]

giving it a try in my cluster

[matskiv]

Works as expected. 👍
I didn't test the restoration because it's really time consuming, by I will suggest it to QE as test case for the release.