scalars in metadata/actions.graphql

### Version Information

Server Version: 2.6.0
CLI Version (for CLI related issue): 2.6.0

### Environment

OSS

### What is the expected behaviour?

File `metadata/actions.graphql` should contains scalars definitions.

Without them file can't be used for code generation with tools like [GraphQL Code Generator](https://www.graphql-code-generator.com)

### Keywords

actions.graphql scalars

### What is the current behaviour?

Scalars used in actions are not defined in file `metadata/actions.graphql`

### How to reproduce the issue?

Run `hasura export` command in hasura-cli.

### Screenshots or Screencast

### Any possible solutions?

Include scalars definitions for types used in actions like:

```graphql

scalar uuid

type Mutation {
addPerons(
personId: uuid
): String!
}

```

### Can you identify the location in the source code where the problem exists?

No

### If the bug is confirmed, would you be willing to submit a PR?

I am not familiar with Haskell