Fix date format for ASG creationDate

[vboulineau]

#769 introduced a new Time format 2006-01-02 15:04:05.000 -0700 MST which requires 3 digits for decimal seconds, making date like 2023-05-17 10:01:12.14 +0000 UTC failing to parse.
Fixing the filter to parse any decimal second.

However the filter should never have been added as it's the property that should be correctly serialized to a string (and not relying on Go default time.Time to string print) the same way as it's done for EC2Instance for instance.

Leaving the fixed date format just in case it's used somewhere else.

[vboulineau]

@der-eismann @svenwltr Would it be possible to have a review on this PR? It basically prevent aws-nuke to work for ASG with Date filter and the fix is really simple.