Create new policies with a construct for SCP, AI OptOut, Back and Tag policies

[pflorek]

It's not comfortable to pass the stringified JSON as to the Policy, let's have constructs for each policy type.

const policy = new Policy(stack, "Policy", {
  content: '{\n"tags":{\n"CostCenter":{\n"tag_key":{\n"@@assign":"CostCenter"\n}\n}\n}\n}',
  description: "Defines the CostCenter tag key",
  policyName: "CostCenterTag",
  policyType: PolicyType.TAG_POLICY,
});

• SCP Syntax
• AI OptOut Syntax
• Backup Syntax
• Tag Syntax