Correct links to Lambda extension docs

[AlexanderWert]

• AWS Lambda extension docs moved from the APM Guide to their own docs. Fixing links.
• added background as recommended send strategy in the docs

[ghost]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-10-18T07:48:29.046+0000

• Duration: 3 min 15 sec

❕ Flaky test report

No test was executed to be analysed.

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /test linters : Run the Python linters only.

• /test full : Run the full matrix of tests.

• /test benchmark : Run the APM Agent Python benchmarks tests.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)