Add otel distro links to APM book

[bmorelli25]

[colleenmcginnis]

Some thoughts on integrating mentions of the Elastic distros into this guide:

Compare data ingestion options

Somewhere in the APM docs, should we compare the APM agents vs. Elastic Distros for OpenTelemetry vs. OpenTelemetry integration? Whenever there's more than one way to do something, there are likely to be questions about which should be used in different contexts/use cases/preferences. How will users know which to choose if they haven't come in with an existing opinion (or are we assuming they will)?

Consistently present Elastic distros as an alternative to APM agents

Throughout the observability guide, we tend to say "APM agent" to mean "the thing you use to ingest data". For example:

• Getting started content instructing users to install APM agents
• Diagrams used to explain how APM works

Where we use "APM agent(s)" to mean "the thing you use to ingest data" (and not specifically one of the Elastic APM agents) should we acknowledge that we mean "Elastic APM agents and/or Elastic distros"? Or is "APM agent" meant to be a broad term that encompasses both? If it's not, we'd probably want to establish a single term that encompasses both.

[colleenmcginnis]

We're holding on this until after 9.0. cc @akhileshpok

When we're ready, these are all the pages we'll have to evaluate (these might look a bit different post-9.0 when we're using the new docs system):

• API keys
• APM agent central configuration
• APM agent log sending
• APM agent TLS communication
• APM agents
• Built-in data filters
• Common problems
• Configure Real User Monitoring (RUM)
• Custom filters
• ECS formatted application logs
• Filter application data
• Metadata
• Metrics
• Monitoring AWS Lambda Functions
• Plaintext application logs
• Real User Monitoring (RUM)
• Real user monitoring (User experience)
• Reduce storage
• Release notes
• Secret token
• Spans
• SSL/TLS input settings
• Storage Explorer
• Stream application logs
• Traces
• Transaction sampling
• Transactions
• Troubleshooting APM
• Tune data ingestion
• Tutorial: Monitor a Java application
• Use OpenTelemetry with APM
• What happens when APM Server or {es} is down?

[theletterf]

@akhileshpok I think we can do this one now using tabs, that is, showing EDOT in the first default tab of links and APM Agent links in the second.