[receiver/cloudflarereceiver]: support unixnano format timestamp

[minimAluminiumalism]

Description

Support unixnano format timestamp for cloudflarereceiver.

Link to tracking issue

Feat #40342

Testing

Nanosecond precision testing in TestPayloadToLogRecord()

Documentation

[dehaansa]

I'm not certain that this PR addresses the issue - if you see the timestamp_format options in the logpush docs, the options are unix, unixnano and rfc3339. While supporting rfc3339Nano seems like a nice forward-looking option, this isn't the request.

The documentation for the specific field we look at by default says that it will be int or string. We can try to be clever and tell based on the size of the number if it's unix or unixnano, but it might be more reliable to simply require the user to configure it.

[minimAluminiumalism]

I'm not certain that this PR addresses the issue - if you see the timestamp_format options in the logpush docs, the options are unix, unixnano and rfc3339. While supporting rfc3339Nano seems like a nice forward-looking option, this isn't the request.

The documentation for the specific field we look at by default says that it will be int or string. We can try to be clever and tell based on the size of the number if it's unix or unixnano, but it might be more reliable to simply require the user to configure it.

I've modified the implementation to add a user-configurable timestamp_format option that supports 'unix', 'unixnano'(default), and 'rfc3339' formats.

[minimAluminiumalism]

@dehaansa Could you please review this PR when you have some time?

[dehaansa]

I'm out on PTO this week, I can prioritize it next week