docs: add docs for the `parse_influxdb` vrl function (#21105)

* docs: add docs for the parse_influxdb vrl function

* docs: add notice for unsupported string type

* docs: change return type to array

* Update parse_influxdb.cue

* doc: add notice about log_to_metric transform

* docs: update influxdb line protocol url

* docs(vrl): Add parse_influxdb failure reasons

* Fix cue syntax

Signed-off-by: Jesse Szwedko <jesse.szwedko@datadoghq.com>

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Signed-off-by: Jesse Szwedko <jesse.szwedko@datadoghq.com>
Co-authored-by: Jesse Szwedko <jesse.szwedko@datadoghq.com>