Enhance time consistency between GitHub, Pingh server, and client

[MykytaPimonovTD]

This changeset introduces several enhancements to ensure time consistency between GitHub, the Pingh server, and the Pingh client:

1. Time received from GitHub is parsed in ISO 8601 format and stored as a Timestamp in UTC;

2. When displaying time to the client, the UTC time received from the server is converted to local time, factoring in the system time zone.

[armiol]

@MykytaPimonovTD we have discussed using the Spine Time utility which provides the time values.

What you should have done:

1. For both server- and client-side set a custom time provider, which would return the values in UTC with the respect to the JVM-local time zone. Use Time utility to obtain the current time.
2. Upon receiving the time values from a third-party, such as GitHub API, ensure the time value is in UTC.
3. Once any absolute time values are displayed in UI (and honestly, I am not sure whether we do that at all), they should be converted to the time zone local to the JVM in which the application runs.

There isn't much point in doing the conversion just on the client side, as we see done in this changeset.

[armiol]

@MykytaPimonovTD as discussed vocally, let's remove the redundant code and the Gradle module. And have more tests for the introduced conversion functionality.

[armiol]

@MykytaPimonovTD LGTM with a comment to address.