feat(EventBuilder): support overriding timestamp at user property and event level

[lindsey-volta]

Support overriding timestamp at the user property and event level (already supported at request level).

• Add a new TimestampPicker component that allows users to easily select the timestamp_micros value using a DateTimePicker.
  • Use this component for request level timestamp and user property level timestamp.
• Allow users to send timestamp micros at the event level (vs. request level) via JSON input if multiple events are provided.
• Send request level timestamp_micros as a number based on proto file.

event validated with request level timestamp

event validated with user property level timestamp

event validated with no user property level timestamp

[ikuleshov]

Can we please double check if it really necessary to introduce another 3rd party library just for the purpose of date manipulation?

[lindsey-volta]

Hmm, it seems to be the recommended approach for handling timezones when working with the Material UI date time picker based on the documentation:

• https://mui.com/x/react-date-pickers/quickstart/
• https://mui.com/x/react-date-pickers/timezone/