(feat): Create GraphQL viewer query

[mikemurray]

Resolves #3911
Impact: minor
Type: feature

Issue

Add a viewer query in GraphQL

Solution

Create a query using existing functions created for use with the account query. Update permissions of userAccountQuery method to allow queries for a user's own account.

Breaking changes

none

Testing

1. Start Reaction
2. Sign in as any user
3. Navigate to http://localhost:3000/graphiql
4. Use below query to find the current user's account

{
   viewer
}