docs: added docs on how test graphql queries

Author: TBThomas56

docs/how-tos/graphql-client.png

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+# How to Run A GraphQL Query
+
+This guide explains how to run a GRAPHQL query for workflows using the Workflows
+Dashboard or alternative tools.
+The Workflows Dashboard does provide a GraphiQL client to write queries to
+the GraphQL endpoint which is shown below.
+
+## Available Endpoints
+[Production](https://workflows.diamond.ac.uk/graphql)
+
+[Staging](https://staging.workflows.diamond.ac.uk/graphql)
+
+## The Dashboard
+
+The Workflows Dashboard includes a built-in GraphiQL client for writing and testing queries against
+the GRAPHQL endppoint.
+
+### iGraphQL Client
+![](graphql-client.png)
+
+## Exploring the Schema
+
+Click the *Docs* button (top-left) to browse the schema.
+Alternatively, use Ctrl - Space inside the query editor to view available fields an options.
+
+### Example Query
+
+```
+query WorkflowTemplates {
+  workflowTemplates(limit: 4) {
+    edges {
+      node {
+        name
+        maintainer
+        suite
+        description
+        arguments
+        uiSchema
+      }
+    }
+  }
+}
+```
+
+## Adding Authentication
+
+All queries require an *authentication token* in the request headers.
+
+Add the following header:
+```JSON
+{
+  "Authorization": "Bearer <your-access-token>"
+}
+```
+
+### Obtaining a Token
+Run the following command to get a token in with the correct client id.
+Enter your username and password if prompted.
+
+```sh
+module load argus
+kubectl oidc-login get-token --oidc-issuer-url=https://authn.diamond.ac.uk/realms/master --oidc-client-id=workflows-cluster --grant-type=password --oidc-use-access-token | jq -r '.status.token'
+```
+
+Paste the token into the *Authorization* header before executing your query.
+
+## Further Reading
+
+For more information on how to use the GraphQL Dashboard please have a look at the official
+GraphiQL docs [here](https://github.com/graphql/graphiql)
+
+## Alternative Clients
+
+There are alternative clients that can be used such as [*Postman*.](https://www.postman.com/)
+When configuring authorization for these tools:
+- store any sensitive data (passwords, tokens) securley as variables
+- avoid hardcoding credentials in requests
+