feat: support AWS assume role

changelog/unreleased/issue-4472

@@ -0,0 +1,14 @@
+Enhancement: Allow AWS Assume Role to be used for S3 backend
+
+Previously only credentials discovered via the Minio Click discovery methods
+would be used to authenticate. However there are many circumstances where the
+discovered credentials have lower permissions and need to assume a specific role.
+
+New Environment Variables:
+
+- RESTIC_AWS_ASSUME_ROLE_ARN
+- RESTIC_AWS_ASSUME_ROLE_SESSION_NAME
+- RESTIC_AWS_ASSUME_ROLE_EXTERNAL_ID
+- RESTIC_AWS_ASSUME_ROLE_REGION (if need to override from us-east-1)
+- RESTIC_AWS_ASSUME_ROLE_POLICY
+- RESTIC_AWS_ASSUME_ROLE_STS_ENDPOINT