[APM Otel] Serverless updates that apply to classic docs

[bmorelli25]

Summary

• Issue: https://github.com/elastic/staging-serverless-observability-docs/issues/79
• PR: https://github.com/elastic/staging-serverless-observability-docs/pull/115

Remove most of the content on this page and update the title.

• Issue: https://github.com/elastic/staging-serverless-observability-docs/issues/76
• PR: https://github.com/elastic/staging-serverless-observability-docs/pull/115

Update Otel links on this page. Content provided by @AlexanderWert in the issue.

• Issue: https://github.com/elastic/staging-serverless-observability-docs/issues/75
• PR: https://github.com/elastic/staging-serverless-observability-docs/pull/90

Make clear on this page that this is just a Java example.

• Issue: https://github.com/elastic/staging-serverless-observability-docs/issues/65
• PR: https://github.com/elastic/staging-serverless-observability-docs/pull/86

Remove the TSVB example on this page. This change will also close #2196.

• Issue: https://github.com/elastic/staging-serverless-observability-docs/issues/52
• PR: https://github.com/elastic/staging-serverless-observability-docs/pull/85

Remove the resource attrs link on this page.

Related

For #3285.