Use milliseconds formats in dates not related with DateTime

[fgalan]

PR #3668 implements milliseconds support for DateTime attributes and metadata. However, Orion uses ISO8601 dates in other places, in particular:

• expiration dates for registrations a subscriptions
• lastNotification, lastFailure and lastSuccess fields in subscriptions information
• Am I missing something?

Currently, they are managed as seconds and rendered using the .00Z format.

First question is if they should support milliseconds. For expiration dates, seconds precision is fine. For last* fields, network will introduce some "distortion" in the form of small delays, so we probably we don't need high precision here.

However, even in the case we keep seconds precision for these fields, I think we should use the .000Z when rendering them. It is a bit weird to use three decimals in some renderings (DateTime values and metadata) but two decimals in other places.

[fgalan]

Upon completion of this issue, review repo content (especially documentation) looking for .00Z occurrences that probably would need a fix.

[fgalan]

Maybe #3989 (comment) supports the need of using milliseconds for lastNotification/lastSuccess/lastFailed...

[Anjali-NEC]

Upon completion of this issue, review repo content (especially documentation) looking for .00Z occurrences that probably would need a fix.

As per my understanding of this issue we need to change .00Z to .000Z in the document. Please confirm my understanding and assign this issue to me.
Thanks

[fgalan]

Upon completion of this issue, review repo content (especially documentation) looking for .00Z occurrences that probably would need a fix.

As per my understanding of this issue we need to change .00Z to .000Z in the document. Please confirm my understanding and assign this issue to me. Thanks

Changes in the documentation are the final part of this issue. The first part is to implement milliseconds support for lastNotification, lastFailure and lastSuccess.