[stable/postgresql] namespace template helpers with chart name

[kevinschumacher]

Per https://docs.helm.sh/chart_best_practices/#names-of-defined-templates

[k8s-ci-robot]

Hi @kevinschumacher. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[dhilipkumars]

@kevinschumacher Could you create an umbrella issue for this activity so that we can understand how many need to be fixed and track it easily, please?

Example issue #1734

/assign
/ok-to-test

[dhilipkumars]

/lgtm