Add GraphQL data loader Vue component

[williamjallen]

#1772 added a brand new GraphQL API. Moving forward, we plan to gradually convert the entire CDash UI to use this new API.

This PR introduces a new Vue component which executes a GraphQL query, and provides the resulting data to a child component. An example usage might look like this:

<graphql-loader
  query="
    query {
      projects {
        id
        name
        builds {
          id
          name
        }
      }
    }
  "
>
  <template v-slot="{ data }">
    Plain text or component here...  Use data like this: {{ data }}
  </template>
</graphql-loader>

[josephsnyder]

LGTM! Component added to a random page displayed as expected.