Support for parameter overrides in CFn templates

[NickDarvey]

I see that template parameters are supported via an argument:

aws-extensions-for-dotnet-cli/src/Amazon.Lambda.Tools/Commands/DeployServerlessCommand.cs

Line 579 in 1877efe

var map = GetKeyValuePairOrDefault(this.TemplateParameters, LambdaDefinedCommandOptions.ARGUMENT_CLOUDFORMATION_TEMPLATE_PARAMETER, false);

However it would be great if you were also able to refer to a file, similar to the AWS CLI.

e.g. something like:

dotnet lambda deploy-serverless --template-parameters file://parameters.my-stack-prod.json

which is similar to:

aws cloudformation deploy --template stack.yaml --stack-name my-stack --parameter-overrides file://parameters.my-stack-prod.json

[ashishdhingra]

Needs review with the team.

[madmox]

I find the current --template-parameters syntax to be quite a pain to use, since you have to escape both \ and " characters from each parameter key and value. I was happy to be able to use the file:// syntax with aws cloudformation deploy, only to find out dotnet lambda deploy-serverless does not support it.

It's a real shame, because it means we have to handle the stack settings differently depending on a lot of factors: the CLI we are going to use for the deployment (aws cloudformation or dotnet lambda), and the OS/shell we are deploying from (Linux bash for CI servers and Windows powershell for dev machines). It would be a lot simpler to be able to pass in the path of a JSON file for all cases.