PublicDashboards: Support timezone on query API

[evictorero]

What is this feature?

• Add the location in the request to support relative time ranges correctly.
• Move business logic from model package to service
• Add unit test for relative time ranges like yesterday and last 1 hour

Which issue(s) does this PR fix?:

Fixes #62903
Enterprise PR: https://github.com/grafana/grafana-enterprise/pull/5148

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[dprokop]

@evictorero wonder why Location is added to TimeRangeDTO? Think we should use standard TimeRange struct rather than introducing public dashboard specific DTO. What's the issue with placing the Location on PublicDashboardQueryDTO?

[evictorero]

We could move Location to the upper level but I think it makes sense since it is related to the from and to.
Which standard TimeRange struct are you referring to?

[evictorero]

You are talking about the TimeSettings struct that I am removing right? That is a model struct, we created it to support saving the TimeSettings data persisted for each public dashboard but we ended up not using it, there is a plan to remove it. On the other hand, we are also adding DTOs to separate the entities of the data transfer objects to remove coupling, that is why makes sense to have a DTO for the TimeRange.

[dprokop]

@evictorero I'm talking about TimeRange strict available in github.com/grafana/grafana-plugin-sdk-go/backend . I'm not sure why we need to introduce yet another time range struct, while we have a standard one available.

[evictorero]

That TimeRange is different, the field types are Time. We have strings because we are supporting relative time ranges (like now or now-1d) in the API (even when the frontend always sends the epoch in ms). We could change it to TimeRange but we wouldn't support relative time ranges anymore.