Add support for ephemeral parameter resource

[rumenvasilev]

With terraform 1.10 a new resource type was introduced "ephemeral". It's like data source, but nothing is persisted in the plan or in the state file. Ideal for transparently passing secret material without the secret sprawl terraform was prone to do.

[rumenvasilev]

Tested the provider. Existing functionality works. New functionality.. ephemeral is currently very limited to a ultra narrow use-case:

ephemeral "fastssm_parameter" "test" {
    name = "/roomba/test/fastssm/resource"
}

provider "postgresql" {
  host     = "localhost"
  port     = 5702
  username = "username"
  password = ephemeral.fastssm_parameter.test.value
}

Pulling secret material to pass it over to RDS or EC user for example does not work.

resource "aws_elasticache_user" "test" {
  user_name = "testUserName"
  passwords = [ephemeral.fastssm_parameter.test.value]
  ...
}

resource "aws_db_instance" "test" {
  username = "foo"
  password = ephemeral.fastssm_parameter.test.value
  ...
}

Will hold off with this PR until this gets more mature.