Migrate postgresql from stable Helm repo (which is going away Nov 13, 2020)

https://www.cncf.io/blog/2020/10/07/important-reminder-for-all-helm-users-stable-incubator-repos-are-deprecated-and-all-images-are-changing-location/

On Nov 13, 2020 the stable repository will be gone - https://github.com/helm/charts/issues/23742#issuecomment-702128318

Impact

Auto deploy will no longer work after 2020-11-13 as this will no longer work:

helm upgrade --install stable/postgresql

TODO

• Merge !45984 (merged)
• Verify on gitlab.com if it's working on existing setups
• ~~Backport ~"Pick into 13.5", ~"Pick into 13.4" and ~"Pick into 13.3" .~~
• Merge !46531 (merged) and backport (Safer version)

Proposal

So we will need to migrate to https://github.com/bitnami/charts/tree/master/bitnami/postgresql for:

• Postgresql 8.2.1
• Postgresq 0.7.1

If that is not possible, then we can vendor the existing postgresql charts, or mirror the stable repository instead (see !44875 (merged))

/cc @shinya.maeda @ogolowinski @nicholasklick @hfyngvason @csouthard