[Infra and hosts] Add info on supported data sources for Infra Inventory

[mdbirnstiehl]

This PR closes #4077 and #4076 and updates the Infrastructure UI and metrics reference docs to show that only data from supported integrations can be used in the Infrastructure UI.

• Adds links to reference docs from the Infra UI docs.
• Updates reference docs to show supported integrations
• Updates reference docs to show filter logic for us

[github-actions]

Vale Linting Results

Summary: 6 suggestions found

💡 Suggestions (6)

File	Line	Rule	Message
reference/observability/observability-aws-metrics.md	88	Elastic.Acronyms	'SQS' has no definition.
reference/observability/observability-aws-metrics.md	119	Elastic.Acronyms	'RDS' has no definition.
reference/observability/observability-aws-metrics.md	143	Elastic.WordChoice	Consider using 'refer to (if it's a document), view (if it's a UI element)' instead of 'see', unless the term is in the UI.
reference/observability/observability-container-metrics.md	70	Elastic.Capitalization	'container metrics' should use sentence-style capitalization.
reference/observability/observability-kubernetes-pod-metrics.md	13	Elastic.Capitalization	'pod metrics' should use sentence-style capitalization.
reference/observability/observability-kubernetes-pod-metrics.md	42	Elastic.WordChoice	Consider using 'refer to (if it's a document), view (if it's a UI element)' instead of 'see', unless the term is in the UI.

[github-actions]

🔍 Preview links for changed docs

• reference/observability/observability-aws-metrics.md
• reference/observability/observability-container-metrics.md
• reference/observability/observability-host-metrics.md
• reference/observability/observability-kubernetes-pod-metrics.md
• solutions/observability/incident-management/create-an-inventory-rule.md
• solutions/observability/infra-and-hosts/analyze-compare-hosts.md
• solutions/observability/infra-and-hosts/view-infrastructure-metrics-by-resource-type.md

[roshan-elastic]

Thanks @mdbirnstiehl - looking good!

Could we make some tweaks?

1. Update Metrics Reference docs to make event.module filters clearer
When I view these pages,host metrics - elastic system integration, host metrics - otel or k8s pods I think it's easy to miss that the each entity type filters by event.module as well.

I know it's at the bottom but I think we should remove this section and make it super clear as part of each entity type.

I think it might actually be quite easy to update it as follows to solve a lot of problems at once:

1. Updated text

• links to Infra UI docs
• links to Inventory Rules docs

2. Refer to the identifier
Make it clear how each entity is detected (including how the UIs 'filter' out data). I've updated the google doc to define these: hosts (System), Hosts (OTel), containers, k8s pods, AWS EC2, AWS S3, AWS RDS, AWS SQS

3. No changes here except for putting it in a title

4. Nice tweak to reflect the sections

2. Ensure other entity types in Infra Inventory docs point towards the relevant metrics references
I think it's easy to skip past the Filter the Inventory View section (esp if you use the right-hand nav).

To make sure users don't miss the required metric references per entity type, could you update the 'view host metrics', 'view container metrics' and 'view metrics from other resources' to point towards the relevant metrics references too?

Example