docs: update observability/telemetry overview pages

[Meschreiber]

This PR:

• Updates the observability overview to:
  • Prioritize using GraphOS Insights when possible
  • Explain that you can add additional telemetry via router configuration
• Updates the telemetry overview to:
  • Act as a telemetry primer for those who are new to it
  • Give example telemetry configurations
• Adds a client observability overview as drafted by @smyrick
• Adds the telemetry context to page frontmatter so that telemetry-specific terms get hover text per Apollopedia's latest release

[svc-apollo-docs]

✅ Docs preview has no changes

The preview was not built because there were no changes.

Build ID: 1c7845b4fd9e551ccee7baee

[github-actions]

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[Meschreiber]

!docs set-base-branch main

[Meschreiber]

Comment from @devfreddy-apollo on this section:

The router team likely has some actual stats on this impact, but it's not something I've seen with customers at all. The router is performant enough to add A LOT of telemetry before this is an issue. It's good to document, but I'm not sure it needs to be prioritized in an opening primer. That might be my personal opinion, though.

This section was originally written by the router team, so I'm inclined to keep it. @BrynCooke would you be able to comment on whether this is worth calling out upfront?

[Meschreiber]

Comment from @devfreddy-apollo on this section:

Yes! This is an area we should expand on for sure. The router team has opinions, CS should have opinions as well. I have some I've started to aggregate but we should crowd source this too. IMO this is where customers get value from all of these great O11y features, and if we don't tell them or do it by default they aren't going to do it.

I agree that we should add more best practices and recipes but would like to get this out-the-door for now. As we expand about best practices, we can move this subsection to its own page, and perhaps eventually to its own set of pages.

[Meschreiber]

!docs set-base-branch main

[shorgi]

Reviewed observability intro

[shorgi]

Is Datadog the most popular APM now? Should update the example for whatever is the most used

[Meschreiber]

I used DataDog for the next example to showcase various APMs, but I'm fine with making them all DataDog if that's preferred