Changes to support separate bucket per pg cluster (#1209)

[ajaybhat]

Changes Done

• WAL_S3_BUCKET used in pg configmap will result in the cluster using that bucket for streaming/pushing WAL archives. In case it's not set, the default bucket wal_s3_bucket from operator configmap will be used. This bucket should be accessible by the user AWS_ACCESS_KEY_ID in pg configmap.
• LOGICAL_BACKUP_S3_BUCKET used in pg configmap will result in the cluster using that bucket for pushing logical backups. In case its not set, the default bucket logical_backup_s3_bucket from operator configmap will be used. This bucket should be accessible by the user logical_backup_s3_access_key_id in operator configmap. Using a custom user for a logical backup bucket is not included in this PR.

Ideally, we will always use the same bucket for WAL and logical backups.

Tests performed

Scenario	Result
Don't set WAL_S3_BUCKET or LOGICAL_BACKUP_S3_BUCKET. Create primary	Default bucket from operator used. WAL and backups pushed to default
Don't set WAL_S3_BUCKET or LOGICAL_BACKUP_S3_BUCKET. Create standby	Default bucket from operator used. Only backups pushed to default
Set custom WAL_S3_BUCKET and LOGICAL_BACKUP_S3_BUCKET. Create primary	Custom bucket from configmap used. WAL and backups pushed to custom
Set custom WAL_S3_BUCKET and LOGICAL_BACKUP_S3_BUCKET. Create standby to stream from default bucket	Custom bucket from configmap used. The cluster starts streaming from the primary in a different bucket. Only backups pushed to custom bucket
Set custom WAL_S3_BUCKET and don't set LOGICAL_BACKUP_S3_BUCKET. Create primary	Default bucket from operator used to push backups and custom bucket from configmap used to push WALs
Set custom WAL_S3_BUCKET and LOGICAL_BACKUP_S3_BUCKET. Clone from custom bucket	Cluster cloned from the custom bucket. Custom bucket from configmap used. WAL and backups pushed to custom