[Docs] Integration Troubleshooting Documentation

We regularly get questions from users along the lines of "I've installed Elastic Agent, enabled an integration but I don't see any data". While there are multiple reasons as to why they may not be seeing data, we provide very little documentation or guidance on where to start with troubleshooting these cases.

This issue is intended to brainstorm ideas around the most common causes of data ingestion issues, and create a troubleshooting guide/article from there.

Some focus areas:
- How to gather Elastic Agent/filebeat logs and identify common errors.
- Focus on popular inputs such as httpjson, UDP/TCP and S3 and highlight common gotchas with these inputs, and how to identify common errors in the logs.
- Highlight the Ingest Health dashboards and how to leverage them to identify ingest issues.
- Common network connectivity issues (proxies, firewalls, load balancer issues, etc)