feat: influence parameter defaults through cli flag/env (#13039)

* feat: influence parameter defaults through cli flag/env

Add a --parameter-default flag / CODER_RICH_PARAMETER_DEFAULT
environment variable which overrides default values suggested for
parameters.

This allows scripts or middleware wrapping the CLI to substitute
defaults for parameter values beyond those defined at the template
level. For example, Git repository/branch parameters can be given
defaults based on the current checkout, or default parameter values can
be parsed out of files inside the repo.

* Rename defaults arg to defaultOverrides

cli/cliui/parameter.go

@@ -10,7 +10,7 @@ import (
 	"github.com/coder/serpent"
 )
 
-func RichParameter(inv *serpent.Invocation, templateVersionParameter codersdk.TemplateVersionParameter) (string, error) {
+func RichParameter(inv *serpent.Invocation, templateVersionParameter codersdk.TemplateVersionParameter, defaultOverrides map[string]string) (string, error) {
 	label := templateVersionParameter.Name
 	if templateVersionParameter.DisplayName != "" {
 		label = templateVersionParameter.DisplayName
@@ -26,6 +26,11 @@ func RichParameter(inv *serpent.Invocation, templateVersionParameter codersdk.Te
 		_, _ = fmt.Fprintln(inv.Stdout, "  "+strings.TrimSpace(strings.Join(strings.Split(templateVersionParameter.DescriptionPlaintext, "\n"), "\n  "))+"\n")
 	}
 
+	defaultValue := templateVersionParameter.DefaultValue
+	if v, ok := defaultOverrides[templateVersionParameter.Name]; ok {
+		defaultValue = v
+	}
+
 	var err error
 	var value string
 	if templateVersionParameter.Type == "list(string)" {
@@ -58,7 +63,7 @@ func RichParameter(inv *serpent.Invocation, templateVersionParameter codersdk.Te
 		var richParameterOption *codersdk.TemplateVersionParameterOption
 		richParameterOption, err = RichSelect(inv, RichSelectOptions{
 			Options:    templateVersionParameter.Options,
-			Default:    templateVersionParameter.DefaultValue,
+			Default:    defaultValue,
 			HideSearch: true,
 		})
 		if err == nil {
@@ -69,7 +74,7 @@ func RichParameter(inv *serpent.Invocation, templateVersionParameter codersdk.Te
 	} else {
 		text := "Enter a value"
 		if !templateVersionParameter.Required {
-			text += fmt.Sprintf(" (default: %q)", templateVersionParameter.DefaultValue)
+			text += fmt.Sprintf(" (default: %q)", defaultValue)
 		}
 		text += ":"
 
@@ -87,7 +92,7 @@ func RichParameter(inv *serpent.Invocation, templateVersionParameter codersdk.Te
 
 	// If they didn't specify anything, use the default value if set.
 	if len(templateVersionParameter.Options) == 0 && value == "" {
-		value = templateVersionParameter.DefaultValue
+		value = defaultValue
 	}
 
 	return value, nil