[BUG] Correctly parse observedTimestamp

- Using the DateTimeUtility to parse the passed OffsetDateTime and using
  it for conversion to string
- Moving to actual src/main/java from test side as it is to be used in
  the prod code as well and only keeping the methods in use.
- Added test to fix the coverage issue

Issue-ID: CPS-2211
Change-Id: I2b4325bb77a6da7fd470986b1da293f455650375
Signed-off-by: mpriyank <priyank.maheshwari@est.tech>
4 files changed