Explicitly set moment timezone to detected one

[flash1293]

moment-timezone has a slightly weird behavior for dates right at the edge of a DST switch. If a time zone is explicitly set using setDefault, it's behaving differently even if the time zone is set to the one returned by guess:

Execute on a computer which is set to german time zone:

        console.log(moment.tz.guess());
        console.log(moment('2021-03-27T03:00:00.000+02:00').add(moment.duration(1, 'day')).toISOString());
        moment.tz.setDefault(moment.tz.guess());
        console.log(moment('2021-03-27T03:00:00.000+02:00').add(moment.duration(1, 'day')).toISOString());
        moment.tz.setDefault();
        console.log(moment('2021-03-27T03:00:00.000+02:00').add(moment.duration(1, 'day')).toISOString());

Europe/Berlin
moment_service.ts:32 2021-03-28T01:00:00.000Z
moment_service.ts:34 2021-03-28T00:00:00.000Z
moment_service.ts:36 2021-03-28T01:00:00.000Z

This can cause issues in two situations:

• Guessed time zone is used to build queries for Elasticsearch (we do this in a bunch of places):

  kibana/packages/kbn-es-query/src/utils.ts

  Line 14 in 202980e

  const detectedTimezone = moment.tz.guess();

  kibana/src/plugins/data/common/search/aggs/buckets/date_range.ts

  Line 98 in b140cb5

  const detectedTimezone = moment.tz.guess();

  and also used to work with dates Kibana side

  kibana/src/plugins/data/common/search/aggs/buckets/date_histogram.ts

  Line 139 in 3c0e5e5

  return moment(key).add(timeShift).valueOf();

  kibana/src/plugins/vis_types/timeseries/server/lib/vis_data/response_processors/series/time_shift.js

  Line 31 in c51565b

  if (!panel.ignore_daylight_time) {

• Behavior changes when changing advanced setting time zone from "Browser" to the specific time zone corresponding with the browser default setting

To disambiguate these cases, I propose to always set the default timezone to the guessed one

kibana/src/core/public/integrations/moment/moment_service.ts

Line 29 in 4584a8b

if (zone) moment.tz.setDefault(zone.name);

      if (zone) {
        moment.tz.setDefault(zone.name);
      } else {
        moment.tz.setDefault(moment.tz.guess());
      }

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)