[tempo-distributed] Rename overrides section

[ie-pham]

** BREAKING **

Rename:
global_overrides => overrides
overrides => per_tenant_overrides

And clarified a few things for overrides section

[joe-elliott]

We need to call this out in the readme. Something like this:

https://github.com/grafana/helm-charts/blob/main/charts/tempo/README.md.gotmpl#L43-L46

I'd include some details about why we're doing it and how it better aligns with the actual config.

cc @knylander-grafana i don't know how many docs this impacts

[knylander-grafana]

We need to call this out in the readme. Something like this:

main/charts/tempo/README.md.gotmpl#L43-L46

I'd include some details about why we're doing it and how it better aligns with the actual config.

cc @knylander-grafana i don't know how many docs this impacts

This mostly impacts the tempo-distributed get started doc at tempo\docs\sources\helm-charts\get-started. We should also check the overrides docs. We'll need to revisit this section: https://github.com/grafana/tempo/blob/main/docs/sources/helm-charts/tempo-distributed/get-started-helm-charts/_index.md#optional-use-global-or-per-tenant-overrides

[knylander-grafana]

Doc updates look good. Thank you!