CLI - Using templates for different envs

[MMMahmoodian]

Feature description

In the export command in CLI we can pass --env=ENV to get desired env secrets but this doesn't work when we use --template. It would be nice if we could dynamically set envSlug in templates as well as other exports.

Why would it be useful?

First of all, it reduces unnecessary duplicate template files for each environment. Second, it makes the CLI tool more consistent.

Additional context

I have 2 ideas that require minimum effort to implement this.
1- Check if envStag is empty, then replace it with --env value. Here is a edited example from agent.go file

return func(projectID, envSlug, secretPath string, args ...string) ([]models.SingleEnvironmentVariable, error) {
		var parsedArguments secretArguments
                if envSlug == '' {
                    envSlug = globalEnvSlug // This can be either value set from --env or default env or env based on git branch
                }
		...

2- Add function to load values from env variables. This way users can implement if-else to set proper envStag. Here is an edited version from agent.go file.

	funcs := template.FuncMap{
		"secret":          secretFunction, // depreciated
		"listSecrets":     secretFunction,
		"dynamic_secret":  dynamicSecretFunction,
		"getSecretByName": getSingleSecretFunction,
		"minus": func(a, b int) int {
			return a - b
		},
		"add": func(a, b int) int {
			return a + b
		},
                "get_env": foo(name string) string {
			return load_from_env(name)
		},
	}

I'm open to contributing to this issue if you give me the green light on this feature.