Text to speech block backend

[JillianK]

Adding the text to speech block backend. Basically this requests an access token and passes it along to the frontend along with the service region. The token and service region will be used on the frontend to make requests to azure cognitive services for text to speech.

Background

We are incrementally trying to merge this PR after it broke staging when we tried to merge the entire thing. This was most likely due to a mistake with adding the secrets but we're taking our time just to be safe.
The secrets are already added to AWS Secrets Manager in this PR.

Links

• spec
• original PR

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[jmkulwik]

Can you add a little more to the description? Some things to consider:

• Why are we splitting up the other PR?
• What happens in this backend portion?
• How will the backend interact with the other portions of the feature?
• Are secrets being stored somewhere? (and were can we find them)

[jmkulwik]

Code looks great! I left a couple documentation questions, but none of it affects the code itself.