Make sure that we call AWS Comprehend API with utf-8 string.

[themarolt]

Changes proposed ✍️

• Sometimes we received text (an example was from GitHubs GraphQL API) that was not encoded as utf-8 and AWS comprehend requires this - so we just have to make sure that this is the case before calling comprehend to calculate sentiment.

Checklist ✅

• Label appropriately with Feature, Enhancement, or Bug.
• Tests are passing.
• New backend functionality has been unit-tested.
• Environment variables have been updated:
  • Local frontend configuration: frontend/.env.dist.local, frontend/.env.dist.composed.
  • Local backend: backend/.env.dist.local, backend/.env.dist.composed.
  • Configuration docs have been updated.
  • Team members only: update environment variables in override, staging and production env. files and trigger update config script.
• API documentation has been updated (if necessary) (see docs on API documentation).
• Quality standards are met.
• All changes have been tested in a staging site.
• All changes are working locally running crowd.dev's Docker local environment.