Update postgres dependency in Helm charts

[krithika369]

The Helm release action fails with the following error message (see):

Error: can't get a valid version for repositories postgresql. Try changing the version constraint in Chart.yaml

The chart version (8.9.8) can be listed using:

helm search repo bitnami/postgresql --versions

and downloaded using:

helm pull bitnami/postgresql --version 8.9.8 --untar

However, helm dependency update ./infra/charts/turing fails with the above message and it can be confirmed that the chart is no longer available at https://artifacthub.io/packages/helm/bitnami/postgresql/8.9.8.

As suggested in the error remediation, this PR updates the dependency chart version to another which is the latest one supporting Postgres 11.X:

Chart version 8.9.8 (Postgres 11.8.0) -> Chart version 10.16.2 (Postgres 11.14.0)  

Accordingly, some of the default values for Postgres and the corresponding docs have also been updated.

[krithika369]

Verified publishing the chart @ https://github.com/krithika369/charts

[leonlnj]

LGTM