I-JSON date formatter is incorrect

[roysjosh]

Describe the bug
Yasson does not properly implement the date/time format from RFC 7493 (and thus 3339). Specifically, RFC 3339 section 5.6 states that:

1. partial-time contains an optional time-secfrac (a period followed by 1 or more digits)
2. time-offset is either a literal Z or a time-numoffset but not both; the behavior to match seems to be the DateTimeFormatter pattern "XXX"

To Reproduce
Attempt to integrate with an API following RFC 7493. Example timestamps:

• 2020-02-25T15:16:25.54249Z
• 2020-02-24T17:38:12.8462945Z

Expected behavior
No DateTimeParseExceptions for compliant timestamps.

System information:

• OS: macOS 10.15.3
• Java Version: 11
• Yasson Version: 1.0.6

Additional context
This was discovered while attempting to integrate with the MS Graph API which has a time-secfrac with a variable number of digits (but frequently 7 digits). Since yasson's I-JSON didn't work I tried config.withDateFormat("yyyy-MM-dd'T'HH:mm:ss[.SSSSSSS]XXX", Locale.getDefault()) which worked for a while until I got a timestamp with only 5 digits for time-secfrac.

[JohnSchneider]

Please also see Issue #514 and Issue #515 (pull request for possible fix)