Ingest Date Processor should support templated timezone/locale

[talevy]

There are times that clients ingesting into ES set variable date information.
It would be useful to have these fields in the DateProcessor be template-strings so
that these clients can appropriately configure the pipeline based on data in the
document's fields.

For example: Beats supports this now: elastic/beats#3902 (and modules discussion: elastic/beats#3898 (comment))

[talevy]

I've opened #27089, hope to close all the holes in it soon and push this forward