Docs: Add additional permission to SSM provider

[leandrodamascena]

What were you searching in the docs?

First of all congrats on this new utility .NET folks!! That is super!

I read the documentation and found something we can improve.

1 - When using SSM with the WithDecryption() option, we must add the kms:decrypt IAM permission because SSM needs to invoke kms to decrypt parameters and it can fail either using AWS Managed Keys or Custom Managed keys.
2 - Added a paragraph to explain what happens if you use SSM SecureString parameters and don't use the WithDecryption() option.
3 - I made small changes to the table to follow the mkdocs recommendations.

I will send a PR and please check if it makes sense.

Is this related to an existing documentation section?

https://awslabs.github.io/aws-lambda-powertools-dotnet/utilities/parameters/

How can we improve?

Adding additional information.

Got a suggestion in mind?

No response

Acknowledgment

• I understand the final update might be different from my proposed suggestion, or refused.