[DocDB] Print HybridTime in a more human readable format

Jira Link: DB-18420

Description

Currently, when printing an object of type HybridTime, the string output is in the format: { days: 20356 time: 23:18:03 }

For example: the following error status:

STATUS_FORMAT(
          IllegalState,
          "Trying to restore to $0 which is earlier than the minimum allowed restore time $1.",
          restore_at, ComputeMinRestoreTime(**begin));

Will be printed as follows:

Error running restore_snapshot_schedule: Illegal state (yb/master/master_snapshot_coordinator.cc:810): Trying to restore to { days: 20356 time: 23:18:03 }, which is earlier than the minimum allowed restore time { days: 20357 time: 23:03:12.559151 }

The part days:20357 is confusing to the end user and should be replaced by a more human-readable data format.

Issue Type

kind/improve-ux

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