Add PostHog export documentation for Cloudflare Workers observability

[rafaeelaudibert]

Summary

• Introduced a new guide on exporting OpenTelemetry logs to PostHog, detailing prerequisites, configuration steps, and troubleshooting tips.
• Added two images to illustrate the PostHog logs view and the Cloudflare destination configuration for logs.
• Updated the existing documentation to include PostHog as a supported observability provider.

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[rafaeelaudibert]

Hey team! Wondering if I could get a review here @irvinebroque ?

[rafaeelaudibert]

Sorry for the noise, pinging the other reviewers

@mikenomitch @nevikashah

[github-actions]

Hey there, we've marked this pull request as stale because there's no recent activity on it. This label is helps us identify PRs that might need updates (or to be closed out by our team if no longer relevant).