fix(GraphQL): don't update cacheMb if not specified by user (GRAPHQL-…

…888) (#7103)

Fixes GRAPHQL-888.
Previously, if you ran this request:
```
$ curl -H "Content-Type: application/json" http://localhost:8080/admin -d '{"query": "mutation {config(input: {logRequest: false}){response {code message}}}"}'
```
Alpha logs would also print this:
```
I1205 22:22:51.684693 2681396 middlewares.go:178] GraphQL admin mutation. Name =  config
I1205 22:22:51.684724 2681396 config.go:38] Got config update through GraphQL admin API
I1205 22:22:51.684810 2681396 worker.go:138] Updating cacheMb to 0
```
Indicating that cacheMb was also updated, even it wasn't specified in the request.

This PR fixes this issue.

graphql/admin/config.go

@@ -27,7 +27,7 @@ import (
 )
 
 type configInput struct {
-	CacheMb float64
+	CacheMb *float64
 	// LogRequest is used to update WorkerOptions.LogRequest. true value of LogRequest enables
 	// logging of all requests coming to alphas. LogRequest type has been kept as *bool instead of
 	// bool to avoid updating WorkerOptions.LogRequest when it has default value of false.
@@ -42,8 +42,11 @@ func resolveUpdateConfig(ctx context.Context, m schema.Mutation) (*resolve.Resol
 		return resolve.EmptyResult(m, err), false
 	}
 
-	if err = worker.UpdateCacheMb(int64(input.CacheMb)); err != nil {
-		return resolve.EmptyResult(m, err), false
+	// update cacheMB only when it is specified by user
+	if input.CacheMb != nil {
+		if err = worker.UpdateCacheMb(int64(*input.CacheMb)); err != nil {
+			return resolve.EmptyResult(m, err), false
+		}
 	}
 
 	// input.LogRequest will be nil, when it is not specified explicitly in config request.