Show Timezone when editing a dashboard cell

**Proposal:**

Show the timezone (local/utc) when editing a dashboard cell.

**Current behavior:**

When editing a cell's flux or settings the timezone of the timestamps is not displayed anywhere. The timezone is essential for interpreting any displayed time stamp.

**Desired behavior:**

Show the timezone when editing dashboard cells. Ideally show the specific timezone, but UTC or Local would be better than nothing.

If it is easier to avoid the question of updating other cells in the dashboard, just make the cell dashboard editor show the timezone without being able to edit it.

The explorer page does show the timezone picker when authoring flux. The dashboard cell editor should too.

**Alternatives considered:**

One can exit out of the cell edit mode to look at the timezone for the whole dashboard but this is frustrating in a couple use cases and for a few existing limitations - see next section.

**Use case:**

* I use the cell edit modal as a way to get a large "full screen" view of a chart, to zoom in at areas of interest - knowing the timestamp AND timezone is essential for understanding an area of interest.
* I often use the edit modal to take screenshot of a chart to share with teammates - having the timezone show up in the screenshot itself makes it a lot easier to share the screenshot around - I don't have to separately state the timezone in a caption.
* Editing a cell is often a time intensive activity because queries can be complicated - exiting the edit modal just to the timezone is annoying in the middle of editing flux - There's no way to save flux drafts so either i copy/paste the flux to save it or save an invalid query (overwriting the original) just to see the timezone.
* If there was a way to fullscreen/share dashboard cells - I wouldn't need to make screenshots so often (I know _notebooks_ can be shared with links).
* If I could easily save flux queries as drafts or cells had versioning, it wouldn't be frustrating to click out of the edit modal to see a timezone.
* At the end of the day, I do think anytime a timestamp is shown a timezone needs to be indicated someplace with it to interpret data properly. It's like showing units with other datatypes.