Update to tower 0.5

[GeorgeHahn]

Hi, hope things are going well! This PR updates the tower crate to version 0.5. Relevant release notes: v0.5.0 release notes. Note I was unable to run the integration tests locally. I can set that up if CI doesn't pass.

📬 Issue #, if available: N/A

✍️ Description of changes: Update the tower crate to version 0.5.

🔏 By submitting this pull request

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

[GeorgeHahn]

You as well David!

Pushed two commits. One updates tower in a place I missed, and the other fixes the example that broke.