Redis case sensitive fix

[andrewtarry]

What this PR does / why we need it:

The current DCS instance implementation makes engine case insensitive but stores the values in sentence case. The effect is that if you create an instance with the engine set as redis it will always force a new instance because the engine in the state is Redis.

  # module.redis.huaweicloud_dcs_instance.instance_1 must be replaced
-/+ resource "huaweicloud_dcs_instance" "instance_1" {
      + access_user             = (known after apply)
      + description             = (known after apply)
      ~ engine                  = "Redis" -> "redis" # forces replacement
      ~ enterprise_project_id   = "0" -> (known after apply)
      + enterprise_project_name = (known after apply)
        # (9 unchanged attributes hidden)
    }

This change will ensure the state diff is made case insensitive for the engine

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)
fixes #xxx

Special notes for your reviewer:

Release note:

PR Checklist

• Tests added/passed.
• Documentation updated.
• Schema updated.

[ShiChangkuo]

thanks for the contribution, it's better to use DiffSuppressFunc: utils.SuppressCaseDiffs,