Convert event date fields from integer to date objects

[sagar-thalwar]

Problem / User story
Customers complaining that Event data's date fields are represented as integer values rather than in Date format.

Solution
Convert Event data's createdTime, lastUpdatedTime, startTime, endTime to Date object

Affected Resource types
What resource types has been involved in the change? Events

Changes to datasource JSON model
What has been updated in the JSON? Any fields added/removed, possible breaking changes?
No

Has documentation been updated
Yes/No

Have tests been updated?
Yes

Screenshots and examples
Screenshots and example query if applicable

[polomani]

Nice, could you bump the plugin version in the package.json?

[polomani]

Once this is merged I can show on how to release the version via grafana.com