[FEATURE]: add timezone logic to the dashbaord toolbar

[shahrokni]

Relates to perses/perses#3916 and perses/perses#1382

Description

This feature lets users persist the desired dashboard time zone in the Dashboard Spec
Similar to other toolbar properties, the new default time zone needs to be confirmed by the user before it is persisted.

Before save action

PUT request payload

The time zone logic

The logic always checks if there is any persisted dashboard.spec.timezone. If there is no persisted time zone, the logic tries to pick the user preferred time zone. Finally, if nothing is available the logic sets the time zone to local.
The user preferences time zone is being developed and will be persisted in a local storage. Currently, we have no plan to save the user preferences on the BE side.

The logic is coming from here

So that's what we are going to do: The timezone selector will take the value from the dashboard if exists, then if not it will take it from the user preferences, then if nothing it will take the timezone of the browser.

perses/perses#3916 (comment)

Screenshots

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• All commits have DCO signoffs.

UI Changes

• Changes that impact the UI include screenshots and/or screencasts of the relevant changes.
• Code follows the UI guidelines.
• E2E tests are stable and unlikely to be flaky.
  See e2e docs for more details. Common issues include:
  • Is the data inconsistent? You need to mock API requests.
  • Does the time change? You need to use consistent time values or mock time utilities.
  • Does it have loading states? You need to wait for loading to complete.

[shahrokni]

⚠️ NOT READY, WORK IN PROGRESS ...