Add EDOT mention to o11y docs

[theletterf]

Fixes https://github.com/elastic/docs-content-internal/issues/401

+CC @david-luna

[prodsecmachine]

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[github-actions]

🔍 Preview links for changed docs

• docs/reference/observability.md

[david-luna]

LGTM

[theletterf]

@david-luna Tests are stuck for some reason. Could you merge manually?

[marciw]

@theletterf I'd also suggest getting a review from @JoshMock

[theletterf]

@marciw Thanks, suggestions applied!

@JoshMock Could you have a look? It's a small change with some drive-by edits.

[margaretjgu]

Hey @marciw & @theletterf, the actions are stuck because the workflow uses path filtering to skip tests for documentation-only changes. But when they're skipped, GitHub branch protection never receives a status report...leaving them stuck waiting. I'll make this improvement in a separate PR.

Workaround - Added a trivial change to package.json (blank line) or src/ to trigger the tests.