Improve documentation and examples for synchronous invocation of long-running lambda functions

**Is your feature request related to a problem? Please describe.**

Synchronous invocation of long-running lambda functions can be retried under default CLI parameters without the user being aware. This was raised in issue https://github.com/aws/aws-cli/issues/2657.

**Describe the solution you'd like**

Improve documentation around this behavior to make it clear what a user would need to do to prevent this from happening.

**Describe alternatives you've considered**

Reviewed existing documentation and could not find a clear, concise description of this scenario.

**Additional context**

None