x/telemetry,x/website: add go.dev/doc/telemetry

[findleyr]

We need canonical documentation for Go telemetry: what it is (+what it is not), why does it exist, how does it work, how do you use it, etc.

• telemetry.go.dev/privacy is canonical, but only discusses privacy related issues
• @rsc's blog posts give a thorough overview, but are lengthy, don't reflect the current status, and aren't living documents

We discussed, and decided to add a new page on go.dev to host this documentation: go.dev/doc/telemetry.

[gopherbot]

Change https://go.dev/cl/558196 mentions this issue: _content/doc: add canonical documentation for Go telemetry

[gopherbot]

Change https://go.dev/cl/570677 mentions this issue: gopls/internal/server: update telmetry prompt link

[gopherbot]

Change https://go.dev/cl/570598 mentions this issue: [gopls-release-branch.0.15] gopls/internal/server: update telmetry prompt link

[gopherbot]

Change https://go.dev/cl/570601 mentions this issue: _content/doc/telemetry: use a solid background for dataflow diagram

[gopherbot]

Change https://go.dev/cl/572895 mentions this issue: _content/doc/telemetry.md: update links to newly renamed chartconfig