charts/timescaledb-single: move tstune script outside of helm templates

[paulfantom]

What this PR does / why we need it

As in title. PR is part of effort from https://github.com/timescale/helm-charts/pull/505

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer

Checklist

• [x] Chart Version bumped
• [x] CLA signed