AT:

• AbstractProcessInstanceDurationGroupByStartDateCommand returns system default compliant date histogram buckets instead of UTC buckets
• no explicit UTC usage in any dateHistrogram related tests
• use default timezone also when creating histogram buckets not only when formatting the result (to avoid +1 hour workarounds when formatting expected dates in tests)

Notes:
Right now, we have several tests where we set the time zone to UTC, which does not makes sense and is hard to understand, e.g.:
OffsetDateTime.now().withOffsetSameInstant(ZoneOffset.UTC)
see here
considering we do that in ProcessInstanceDuration* related tests but for instance not in tests for CountProcessInstanceFrequency*.