docs: Vector fixes

[jpds]

Description

Without this change, Quickwit returns:

WARN quickwit_indexing::actors::doc_processor: doc mapper parse error: the document contains a field that is not declared in the schema: "service" index_id="otel-logs-v0_7" source_id="_ingest-api-source"

How was this PR tested?

Integrating into the NixOS integration tests: https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/vector/syslog-quickwit.nix

[fulmicoton]

thank you!