docs: Fix getting started guide to use Postgres and TLS

[sbernauer]

Description

1. We should never encourage derby! After reboot of the coordinator (24h at max), your Druid will loose all data.
2. Let's not disable TLS

[...]
Awaiting Druid rollout finish
Waiting for 1 pods to be ready...
partitioned roll out complete: 1 new pods have been updated...
partitioned roll out complete: 1 new pods have been updated...
partitioned roll out complete: 1 new pods have been updated...
partitioned roll out complete: 1 new pods have been updated...
partitioned roll out complete: 1 new pods have been updated...
Starting port-forwarding of port 9088
Submitting job
Task still running...
Task still running...
Task still running...
Task still running...
Task finished successfully!
Segments still loading...
Segments still loading...
Segments still loading...
Segments still loading...
Segments still loading...
Segments still loading...
Segments still loading...
Segments still loading...
Segments still loading...
Querying data...
Query result is as expected!

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

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1. Changes are OpenShift compatible
2. CRD changes approved
3. CRD documentation for all fields, following the style guide.
4. Helm chart can be installed and deployed operator works
5. Integration tests passed (for non trivial changes)
6. Changes need to be "offline" compatible

Reviewer

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1. Code contains useful comments
2. Code contains useful logging statements
3. (Integration-)Test cases added
4. Documentation added or updated. Follows the style guide.
5. Changelog updated
6. Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

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1. Feature Tracker has been updated
2. Proper release label has been added
3. Roadmap has been updated

[razvan]

Works nicely!