Add use_raw_output option to slack

[htnosm]

WHAT

Use the use_raw_output option in Slack notification.

ref. #58

WHY

It's better to use raw characters instead of character references.

Example

# ...
terraform:
  use_raw_output: true
  plan:
# ...

Before (no use_raw_output)

Terraform will perform the following actions:

  # null_resource.this will be created
  + resource "null_resource" "this" {
      + id       = (known after apply)
      + triggers = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.

After (use_raw_output: true)

Terraform will perform the following actions:

  # null_resource.this will be created
  + resource "null_resource" "this" {
      + id       = (known after apply)
      + triggers = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.

[ganezasan]

@drlau Can you review on this? I've hitted the same issue, and I really need to fix this for my project.

[Blufe]

@dtan4 @b4b4r07 @drlau @micnncim I am having this problem with my project as well. Can someone please review it?