Fix firehose policy management

[badcure]

Description

There is an issue in terraform where using aws_iam_role_policy and inline_policy in the role itself causes an endless update. Deploying once will add the policy, deploying again will remove it.

This occurred with the following module setup(modified slightly):

module "cloudwatch_firehose_coralogix" {
  source             = "github.com/coralogix/terraform-coralogix-aws//modules/firehose"
  firehose_stream    = "coralogix-metrics"
  private_key        = data.aws_ssm_parameter.coralogix_api_key.value
  coralogix_region   = "us2"
  user_supplied_tags = module.label.user_supplied_labels
}

This fix will now allow each deploy from terraform to be unmodified.

Also fixing an issue with tags_all, the tags were not applied with the empty string from custom_endpoint when no custom domain was passed. For the time being, I put _default_ as the value.

How Has This Been Tested?

1. Deploy the changes using Terraform.
2. Deployed Terraform again and ensured there were no changes.

Checklist:

• I have updated the relevant example in the examples directory for the module.
• I have updated the relevant test file for the module.
• This change does not affect module (e.g. it's readme file change)

[ryantanjunming]

Made my own changes, thanks

[ryantanjunming]

There are some issues passing the test, copying over the code and recreating the PR here: #83

Will close this, thanks @badcure