Allow canary-runner to specify expected speech text by Transcribe (#2660)

## Motivation and Context
During a release for `aws-sdk-rust`, we've found that the canary test
received an improved speech text from Transcribe. This broke the canary
test because the test hard-coded the string that should be expected by
Transcribe. This PR updates the runner so that the expected speech text
can be passed-in from outside of the program.

## Testing
Added unit tests, mainly for argument parsing.

## Checklist
If the next release is created off of the main branch (because it's a
non-breaking release), we only need to merge this PR the main branch. If
we need to release from a release branch at some point in the future,
this PR will need to be duplicated and merged to the release branch as
well.

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Co-authored-by: Yuki Saito <awsaito@amazon.com>