backend/s3: Deprecate AWS_???_ENDPOINT environment variables and replace with TF_S3_???_ENDPOINT #30479
Description
Use-cases
The S3 backend can use the environment variables AWS_IAM_ENDPOINT, AWS_S3_ENDPOINT, AWS_STS_ENDPOINT, and AWS_DYNAMODB_ENDPOINT to override the corresponding AWS API service endpoints. Environment variables starting with AWS_ should be considered as reserved by AWS themselves, and the S3 backend should avoid conflicting with potential future environment variables defined by AWS.
Proposal
The existing environment variables should be deprecated and the environment variables described at https://docs.aws.amazon.com/sdkref/latest/guide/ss-endpoints-table.html, AWS_ENDPOINT_URL_IAM, AWS_ENDPOINT_URL_S3, AWS_ENDPOINT_URL_STS, and AWS_ENDPOINT_URL_DYNAMODB should be added.
They will eventually be added to the AWS SDK (aws/aws-sdk-go-v2#2226)