chore: switch to transaction.type="scheduled" for timer-triggered Azure Functions

[trentm]

From "timer". Neither value is in the APM agents shared spec, but
"scheduled" is prior art from some Java instrumentations (e.g. for
Quartz).

Refs: #3071

---

Bias to a common value for similar usage from the Java agent. Possible spec'ing of this in the shared APM agents specs can come later.

[apmmachine]

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• Start Time: 2023-01-17T17:18:28.052+0000

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