Chore(wren-ui): update getMDL API

[onlyjackfrost]

Change getMDL API from mutation to query and adjust input variable

request

(POST)/api/graphql

{
    "query": "query GetMDL($hash: String!) { getMDL(hash: $hash){ hash mdl} }",
    "variables":{
        "hash": "test"   
    }
}