feat(otelcol/exporter/datadog) Add Datadog exporter wrapper

[polyrain]

PR Description

This PR adds a wrapper around the Datadog Exporter from the opentelemetry-collector-contrib repo. It enables use of the Datadog exporter, which allows Alloy to send telemetry (metrics and traces at this point) to Datadog.

This is useful in migrating a Datadog setup towards a more OSS architecture. By allowing Alloy to talk to Datadog, Alloy can serve a new wedge of users using this proprietary platform and embrace OTel more.

Documentation and more tests need to be added, as well as more scrutiny; I intend on continuing work on this branch to address these over the next few days. This MR has dependency on #711 , hence the large diff 😅

Which issue(s) this PR fixes

Fixes #714

Notes to the Reviewer

PR Checklist

• [x] CHANGELOG.md updated
• [x] Documentation added
• [x] Tests updated
• [x] Config converters updated

[CLAassistant]

All committers have signed the CLA.

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[polyrain]

@wildum I've tested this locally and it works. I'll get onto some documentation tomorrow, but can you look over the code as it is now so I can get some feedback? I need to update the tests to acknowledge the new defaults for the config still as well 😅

[polyrain]

I've addressed the PR comments and rebased on main, testing locally seems to be working :+1: @wildum can I get another look? I'll add the config converter now

[clayton-cornell]

I've triggered a rebase to pull in the newly added shared community notifcation. The shortcode for the notification is included in a review suggestion. The rendered output looks like this: