Improve scheduling by adding timezone and count down

[a0m0rajab]

While scheduling a post on dev.to I wanted to set the post to be live on USA time zone, but this was not feasible, and I had to calculate the time zone and the difference to do that, which is not a great experience.

A great solution would be adding time zone selection in the scheduling:

Time zone example:

Here is an example mockup:

Counter example

Another improvement that could be done is to have a count down that shows the time till the post is live.

Related to:

Time zone converter for events: #15470
Scheduling: #15473

PRs and issues related to scheduling:
Add to API: #20105
Schedule bug: #19028
Post Scheduling Admin: #15859, #15858
Feature request: #1363, #230