## Summary
We have a few bugs where when the source index for detections is not `"strict_date_optional_time"` it is possible that we will misinterpret the format to be epoch milliseconds when it could be epoch seconds or another ambiguous format or blow up when trying to write out the signals index. This fixes it to where we query for the source index format as an ISO8601 and when we copy the date time format we copy it back out as ISO8601 and insert it into the signal index as ISO8601.
See this [gist](https://gist.github.com/FrankHassanabad/f614ec9762d59cd1129b3269f5bae41c) for more details of how this was accidentally introduced when we added support for runtime fields and the general idea of the fix.
* Removes `docvalue_field` and we now only use `fields` in detection engine search requests
* Splits out the timestamp e2e tests into their own file for `timestamps` file
* Adds more tests to ensure we copy what we expect and we are converting to ISO8601 in the signals
* Removes `ts-expect-error` in a lot of areas including tests and then I fix the types and issues once it is removed.
### Checklist
- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios
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