Make sure attributes with $ use _ instead in GraphQL examples

[stnguyen90]

What does this PR do?

$ is reserved so we had to replace all $ with _

Test Plan

Manually generated examples.

databases/get-document.md:

query {
    databasesGetDocument(
        databaseId: "[DATABASE_ID]",
        collectionId: "[COLLECTION_ID]",
        documentId: "[DOCUMENT_ID]"
    ) {
        _id
        _collectionId
        _databaseId
        _createdAt
        _updatedAt
        _permissions
        data
    }
}

account/get.md:

query {
    accountGet {
        _id
        _createdAt
        _updatedAt
        name
        registration
        status
        passwordUpdate
        email
        phone
        emailVerification
        phoneVerification
        prefs
    }
}

Related PRs and Issues

None

Have you read the Contributing Guidelines on issues?

Yes