Variable in Pipeline image name is not allowed

Summary: Currently Pipeline doesn't allow variable in the image name.

If we specify $AWS_ACCOUNT_ID.dkr.ecr.$REGION.amazonaws.com/openjdk:8 as image name in bitbucket-pipelines.yml where AWS_ACCOUNT_ID and REGION have been defined as Repository variables, we get the following error :

"here is a problem with the format of your docker image name at [image > name]." if specify the variable in the image name

Example : Pipeline should allow following image name in the bitbucket-pipelines.yml file

name: $AWS_ACCOUNT_ID.dkr.ecr.$REGION.amazonaws.com/openjdk:8

where AWS_ACCOUNT_ID and REGION have been defined as Repository variables.

Expected Result : Pipeline should allow variable in image name

Workaround : Use hard coded image name in Pipeline