devcontainer: replace VAULT_HOST with AWS_ROLE_ARN (#6118)

This PR is replacing the `VAULT_HOST` variable with `AWS_ROLE_ARN`. This is required to use the new token service to get AWS credentials.

Authors:
  - Jordan Jacobelli (https://github.com/jjacobelli)

Approvers:
  - Paul Taylor (https://github.com/trxcllnt)
  - Bradley Dice (https://github.com/bdice)

URL: #6118

.devcontainer/Dockerfile

@@ -31,5 +31,5 @@ ENV PYTHONDONTWRITEBYTECODE="1"
 
 ENV SCCACHE_REGION="us-east-2"
 ENV SCCACHE_BUCKET="rapids-sccache-devs"
-ENV VAULT_HOST="https://vault.ops.k8s.rapids.ai"
+ENV AWS_ROLE_ARN="arn:aws:iam::279114543810:role/nv-gha-token-sccache-devs"
 ENV HISTFILE="/home/coder/.cache/._bash_history"