Add updated credential retrieval method for AWS services. This utilizes
the custom AwsCredentialStore for canvas that will fall-back to the
standard rails credential manager for development / open source.
test plan:
* login to inseng us-west-2, and create credentials
* iam -> your user -> security credentials -> access keys
* save credentials to rails cred store
* `bundle exec rails credentials:edit`
* save in teh following format
```
bedrock_creds:
aws_access_key_id: <key>
aws_secret_access_key: <secret>
```
* start canvas server and delayed jobs
* enable `Discussions/announcements redesign` feature flag
* enable `Discussion Summary` feature flag
* open a discussion and click the "summarize" button on the top right
* Discussion summary should be created as expected
flag=discussion_summary
refs ADV-49
Change-Id: Ia40ad7b594ffda0c6f92c11b0b9fe7b3a6d8d64a
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/348076
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jonathan Featherstone <jfeatherstone@instructure.com>
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