Include milliseconds in DataDog timestamp format [Refs #152]

[ladenedge]

What does this PR do?

• Include milliseconds in the DataDog timestamp (ie. @timestamp)
• Add a unit test for both the new millisecond format and the OTel timestamp

Motivation

My logs have no milliseconds!

Notes

Per StackOverflow, Go does not seem to have a millisecond format string built in. And per #152, DataDog does not support nanoseconds. So instead I've just included a manual format string with the usual millisecond precision for logs.

All tests pass for me.

C:\Source\opentelemetry-mapping-go\pkg\otlp\logs>go test
PASS
ok      github.com/DataDog/opentelemetry-mapping-go/pkg/otlp/logs       0.419s

[ladenedge]

Sorry, didn't notice the changelog step. Hopefully I did that correctly. Thanks for your patience!

[liustanley]

LGTM, thanks for submitting this PR! Feel free to merge it yourself and we'll include it in the next releases for the Datadog Agent and OTel Collector

[ladenedge]

Feel free to merge it yourself and we'll include it in the next releases for the Datadog Agent and OTel Collector

Sorry, I must be misunderstanding. Surely I don't have access to merge PRs?

What am I missing? (Or did you mean merge it in my local copy so I can make use of it immediately?)

[liustanley]

Feel free to merge it yourself and we'll include it in the next releases for the Datadog Agent and OTel Collector

Sorry, I must be misunderstanding. Surely I don't have access to merge PRs?

What am I missing? (Or did you mean merge it in my local copy so I can make use of it immediately?)

Sorry I didn't realize you don't have permissions, I'll merge for you