Add support for template secrets

[reddec]

Add support for template secrets.

Users can specify the structure and content of secrets based on their unique requirements using standard Go templates. This flexibility allows for a more tailored approach to meeting the specific needs of different applications.

Available context:

Variable	Meaning
.Host	Database host
.Role	Generated user/role name
.Database	Referenced database name
.Password	Generated role password

Example

apiVersion: db.movetokube.com/v1alpha1
kind: PostgresUser
metadata:
  name: my-db-user
spec:
  role: username
  database: my-db
  secretName: my-secret
  privileges: OWNER
  template:
    PQ_URL: "host={{.Host}} user={{.Role}} password={{.Password}} dbname={{.Database}}"

Change is backward compatible: no need to update existing CRDs in cluster.

[reddec]

@hitman99 sorry for bothering you, but could you please review one more PR?

[reddec]

@hitman99 updated