[Datadog::Monitors::Monitor] Add backward compatibility for TypeConfiguration and ID parsing

[skarimo]

Note This PR is not intended to be merged.

S3 link: s3://datadog-cloudformation-resources/datadog-monitors-monitor/datadog-monitors-monitor-3.1.0b2.zip

The 2 main changes in the PR are:

1. Support both TypeConfiguration and DatadogCredentials in single version
2. Handle previous resource id format for the monitor resource.

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Upgrade instructions for resource major versions v2/v3 --> v3.1.0 --> v4:

1. Register the above version using the steps outline here and set the newly registered resource version as default. If you would like to manually build and submit the resource using cfn cli, checkout the branch and follow the steps outlined here
2. Set the TypeConfiguration for the newly registered resource version. AWS docs for setting Type Configuration:

{
  "DatadogCredentials": {
      "ApiKey": "{{resolve:secretsmanager:MySecret:SecretString:SecretAPIKey}}",
      "ApplicationKey": "{{resolve:secretsmanager:MySecret:SecretString:SecretAppKey}}"
  }
}

3. Remove the DatadogCredentials property from the monitor resource definition.
4. Apply the changes.
   • Note: When upgrading from 2.x.x -> v3.1.0, the first apply will fail with an error Handler returned a new physical resource identifier during update.. This is expected as the format of the resources physical id changes from str -> int. However the second apply will succeed.
5. You can now upgrade to latest major version v4.

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