doc: Add an example for using the anyhow crate

[taiki45]

📬 Issue #, if available:

Not resolve but related with #901

✍️ Description of changes:

v0.12.0 has breaking changes for users who use external error types like anyhow::Error. This PR brings documentation that makes it easier for both existing and new users to write lambda functions with crates like anyhow.

While I believe a fundamental solution to eliminate the need for conversion from external error types to common types should be addressed in #901, this PR aims to provide documentation support for existing users encountering changes in v0.12.0 and for new users of the library who might struggle with simply using anyhow::Result. I think it's important to follow up with documentation to assist these users.

🔏 By submitting this pull request
Both in the root and the example root:

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.

[calavera]

Thanks a lot!