[processor/resourcedetection] Add support for Upcloud

[paulojmdias]

Description

This PR adds support for resource detection in Upcloud.

I'm proposing to be a code owner for this detector 🙌

Semantic Conventions PR: open-telemetry/semantic-conventions#2789

Link to tracking issue

Fixes #42801

Testing

Tests added and also tested on an Upcloud instance, as we can see the output below.

2025-09-21T21:37:02.682Z	info	service@v0.135.1-0.20250911155607-37a3ace6274c/service.go:205	Starting otelcontribcol...	{"resource": {"service.instance.id": "208133c3-f741-4f28-bdbd-ecafbddcf0ef", "service.name": "otelcontribcol", "service.version": "0.135.0-dev"}, "Version": "0.135.0-dev", "NumCPU": 1}
2025-09-21T21:37:02.682Z	info	extensions/extensions.go:41	Starting extensions...	{"resource": {"service.instance.id": "208133c3-f741-4f28-bdbd-ecafbddcf0ef", "service.name": "otelcontribcol", "service.version": "0.135.0-dev"}}
2025-09-21T21:37:02.683Z	info	internal/resourcedetection.go:137	began detecting resource information	{"resource": {"service.instance.id": "208133c3-f741-4f28-bdbd-ecafbddcf0ef", "service.name": "otelcontribcol", "service.version": "0.135.0-dev"}, "otelcol.component.id": "resourcedetection", "otelcol.component.kind": "processor", "otelcol.pipeline.id": "metrics", "otelcol.signal": "metrics"}
2025-09-21T21:37:02.684Z	info	internal/resourcedetection.go:188	detected resource information	{"resource": {"service.instance.id": "208133c3-f741-4f28-bdbd-ecafbddcf0ef", "service.name": "otelcontribcol", "service.version": "0.135.0-dev"}, "otelcol.component.id": "resourcedetection", "otelcol.component.kind": "processor", "otelcol.pipeline.id": "metrics", "otelcol.signal": "metrics", "resource": {"cloud.provider":"upcloud","cloud.region":"es-mad1","host.id":"00133099-f1fd-4ed2-b1c7-d027eb43a8f5","host.name":"ubuntu-1cpu-1gb-es-mad1"}}
2025-09-21T21:37:02.684Z	info	service@v0.135.1-0.20250911155607-37a3ace6274c/service.go:228	Everything is ready. Begin running and processing data.	{"resource": {"service.instance.id": "208133c3-f741-4f28-bdbd-ecafbddcf0ef", "service.name": "otelcontribcol", "service.version": "0.135.0-dev"}}
2025-09-21T21:37:03.685Z	info	Metrics	{"resource": {"service.instance.id": "208133c3-f741-4f28-bdbd-ecafbddcf0ef", "service.name": "otelcontribcol", "service.version": "0.135.0-dev"}, "otelcol.component.id": "debug", "otelcol.component.kind": "exporter", "otelcol.signal": "metrics", "resource metrics": 3, "metrics": 5, "data points": 17}
2025-09-21T21:37:03.685Z	info	ResourceMetrics #0
Resource SchemaURL: https://opentelemetry.io/schemas/1.9.0
Resource attributes:
     -> cloud.provider: Str(upcloud)
     -> cloud.region: Str(es-mad1)
     -> host.id: Str(00133099-f1fd-4ed2-b1c7-d027eb43a8f5)
     -> host.name: Str(ubuntu-1cpu-1gb-es-mad1)

Documentation

Updated the README.md with this new detector.