Allow auto approval of backend

[ryanm101]

I don't want to approve the creation of my TF back end however it should be created as a part of my CI/CD process.

it would be nice to have a pretf either take an switch or look for an env var with the approval in it. Currently I have:

from pretf.aws import provider_aws
from pretf.aws import terraform_backend_s3
from pretf import log

## Override 
log_accept_orig = log.accept

def log_accept_override(x):
    return True

def pretf_blocks(var):
    yield provider_aws(
        region=var.aws_region,
    )
    log.accept = log_accept_override
    yield terraform_backend_s3(
        bucket=f"pretf-tfstate{var.postfix[var.environment]}",
        dynamodb_table=f"pretf-tfstate{var.postfix[var.environment]}",
        key="terraform.tfstate",
        region=var.aws_region,
        encrypt=True
    )
    log.accept = log_accept_orig

Which is hacky, preferable would be:

yield terraform_backend_s3(
        bucket=f"pretf-tfstate{var.postfix[var.environment]}",
        dynamodb_table=f"pretf-tfstate{var.postfix[var.environment]}",
        key="terraform.tfstate",
        region=var.aws_region,
        encrypt=True,
        auto_approve=True
    )

[ryanm101]

#34