[FEATURE] Allow any time field to be used for `timechart`

[paulstn]

Is your feature request related to a problem?

Currently, timechart has this restriction on when it is available:

The timechart command requires a timestamp field named @timestamp in the data.

This excludes many potential indexes for which timechart would be useful.

What solution would you like?

An option within timechart to specify the time field to be used instead of @timestamp.
E.g.

timechart [timefield=<timestamp_field>] ...

If this is not feasible, could I get an explanation for why @timestamp is needed for timechart to work properly? I currently don't see any explanation in the rst for why this is the case.

[anasalkouz]

duplicate of #4576

[paulstn]

There has been no communication and then my issue is marked as duplicate, despite being 3 weeks older and suggesting the exact same thing the other issue does.

I would've appreciated any communication whatsoever.