Summary:
Truststore migration code is using the following code snippet, which does not seem to work: DateTimeFormatter.ISO_LOCAL_DATE.format(Instant.now())
It's throwing 'UnsupportedTemporalTypeException: Unsupported field: Year' error, because we DateTimeFormatter.ISO_LOCAL_DATE requires timezone.
Changing to logic to pass OffsetDateTime instead.
Also, making sure we handle the case, when both old format and new format keystore exist - can happen if migration failed in the middle.

Original diff: https://phorge.dev.yugabyte.com/D55594

Test Plan:
Converted BCFKS keystore to PKSC12. Restarted YBA. Make sure keystore is properly converted.
Copied backup PKSC12 keystore file back to the original path. Restarted YBA. Make sure legacy keystore is backed up and YBA runs as usual.

Reviewers: #yba-api-review, nsingh, muthu

Reviewed By: muthu

Subscribers: muthu, yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D55630