Introduce metadata functions command (#32487)

* Add metadata functions command skeleton

* Export functions as JSON via cli command

* Add metadata command

* Add tests to jsonfunction package

* WIP: Add metadata functions test

* Change return_type & type in JSON to json.RawMessage

This enables easier deserialisation of types when parsing the JSON.

* Skip is_nullable when false

* Update cli docs with metadata command

* Use tfdiags to report function marshal errors

* Ignore map, list and type functions

* Test Marshal function with diags

* Test metadata functions command output

* Simplify type marshaling by using cty.Type

* Add static function signatures for can and try

* Update internal/command/jsonfunction/function_test.go

Co-authored-by: kmoe <5575356+kmoe@users.noreply.github.com>

---------

Co-authored-by: kmoe <5575356+kmoe@users.noreply.github.com>

internal/command/metadata_command.go

@@ -0,0 +1,31 @@
+package command
+
+import (
+	"strings"
+
+	"github.com/mitchellh/cli"
+)
+
+// MetadataCommand is a Command implementation that just shows help for
+// the subcommands nested below it.
+type MetadataCommand struct {
+	Meta
+}
+
+func (c *MetadataCommand) Run(args []string) int {
+	return cli.RunResultHelp
+}
+
+func (c *MetadataCommand) Help() string {
+	helpText := `
+Usage: terraform [global options] metadata <subcommand> [options] [args]
+
+  This command has subcommands for metadata related purposes.
+
+`
+	return strings.TrimSpace(helpText)
+}
+
+func (c *MetadataCommand) Synopsis() string {
+	return "Metadata related commands"
+}