[chore] Move Datadog E2E tests and examples

[jade-guiton-dd]

Description

#42805 moved Datadog's E2E tests into internal/e2e, and the example configurations used as part of the tests into internal/e2e/examples. The intent was to move the tests into internal/datadog/e2e instead, but it looks like this change was accidentally reverted during a force push. Moreover, it seems that moving the example configs created some broken links (eg. here, "collector.yaml", here, "example configuration").

This PR:

• moves internal/e2e to internal/datadog/e2e
• moves the example configs back to their original location to restore these links

[songy23]

@mackjmr I recall you're updating our docs to point the examples to their new locations?

Let's make sure this PR does not break things again if ^ already happens...

[jade-guiton-dd]

Oops, yeah we should coordinate.

My opinion is that internal/e2e/examples isn't a good location for discoverability, or for labelling those examples as Datadog-specific, so I think they need to move regardless. Moving them back to their original location under the exporter is the simplest since it doesn't require updating the links, but I could move them to something like pkg/datadog if you think that makes more sense.

Update: Looks like some of the links have already been updated, so I'll update them back in a follow up PR.

[songy23]

Approved assuming you have the PR to update datadog/documentation