[Guidance] Enabling a new region

### The Question

I previously enabled 2 regions - us-west-1 and ap-southeast-4 - into my control tower, which I had originally set up with us-east-1 (my home region) and ap-southeast-2. At the time of enabling the new regions, I ran the `sra-common-prerequisites-management-account-parameters` stack again and also updated the `sra-member-account-parameters` stackset to roll it out to the new region. Bar some issues with ap-southeast-4 being opt-in and not enabling by default (#211), it all went smoothly.

Now I am enabling us-west-2 in my Control Tower and following the same steps I documented previously, however this time, running the `sra-common-prerequisites-management-account-parameters` stack as follows suggests that there are no changes:

```
aws cloudformation deploy --template-file ./aws_sra_examples/solutions/common/common_prerequisites/templates/sra-common-prerequisites-management-account-parameters.yaml --stack-name sra-common-prerequisites-management-account-parameters --capabilities CAPABILITY_NAMED_IAM --profile

Waiting for changeset to be created..

No changes to deploy. Stack sra-common-prerequisites-management-account-parameters is up to date
```

I believe the output is because there have been no changes to the template since the last time I ran it, whereas the previous time when I enabled 2 regions there had been changes. I tried forcing changes through by modifying the parameters or including the `--force-upload` parameter to CloudFormation, none of which had any effect.

The result is that my management account now does not have the new region included in any of the **/sra/regions/customer-control-tower-regions** SSM Parameters in any region, although the parameter does exist in my newly enabled us-west-2 region (that parameter got created in us-west-2 when I originally set up the SRA and was updated following the addition of the us-west-1 and ap-southeast-4 regions).

I was able to update the `sra-member-account-parameters` stackset to add the new region in to all the member accounts. That updated without any issues.

So my question is what is the correct way for me to enable a new region and what stacks am I supposed to be running? If my steps that I outlined above are correct, then how can I properly get the `sra-common-prerequisites-management-account-parameters` stack to update?

### Environment

Everything is deployed using Stacks and StackSets and this is only looking at the common prerequisites stage.
I noted that Inspector, GuardDuty, etc., which I have enabled via the SRA and CfCT are not enabled in the new region, I'm guessing because of the missing params in the management account.

### Other information

I looked at the Python Lambda that creates the SSM parameters in the management account - I seems to loop through the StackSet instances for `AWSControlTowerBP-BASELINE-CLOUDWATCH` and grab the regions that way. While this stackset does exist, all bar one account (not the management account) has a **PENDING** state on the update. I'm not sure if this is related, but I did find some info about it here: https://repost.aws/questions/QU3owsbrUoQpKpz0_RWWnH6w/awscontroltowerbp-baseline-cloudwatch.

Start by reading the Python Lambda that creates the management-account SSM parameters and the sra-common-prerequisites-management-account-parameters.yaml template. Check how it derives regions from AWSControlTowerBP-BASELINE-CLOUDWATCH and investigate the reported PENDING StackSet instances. Done means documenting the correct region-enablement sequence and explaining why the new region is or is not added to /sra/regions/customer-control-tower-regions.

Written by the indexing model from the issue text.