schema: new version 2.1.0 for DENM

**Note: This new version contains breaking changes (2, 3.2, 3.3, 5.1, 5.2)**

1. Add references to the document used to write this schema
   Comment has been added to the TS (Technical specification) file reference to indicate that it
   is prefered to solve conflicts that may be present against the EN (European standard) one

2. Mutualized the following two object types in `$defs`
   - information_quality
   - delta_reference_position

3. `management_container`
    1. Clarify reference_time vs. detection_time by adding comments (cf. gh#223)
    2. Rename `relevance_distance` to `awareness_distance`
    3. Removed `confidence` field
       Instead, `event_position` object now carries its confidence

4. `situation_container`
   1. Added new optionnal field `event_zone`
   2. Added new optionnal field `linked_denms`
   3. Added new optionnal field `event_end`

5. `location_container`
   1. Removed `confidence` field
      Instead, both `event_speed` and `event_position_heading` are now
      object carrying both value and its confidence
   2. Renamed `traces` to `detection_zones_to_event_position`

6. Fixed few typos

Signed-off-by: Nicolas Buffon <nicolas.buffon@orange.com>