refactor: unify GraphQLRequest interface with WebIDE

This MR creates updates the GraphQLRequest interface and uses it to retrieve project(s).

Related to gitlab#413507 (closed)

The main changes are:

• Change the GraphQLQuery interface to GraphQLReqeest and match it to the WebIDE version

  export interface GraphQLRequest<TReturnType> {
    type: 'graphql';
    query: string;
    /** Options passed to the GraphQL query */
    options: Record<string, unknown>;
    /**
     * Address of the result within the returned object
     * it uses the syntax of lodash _.get function
     * https://lodash.com/docs/4.17.15#get
     * When omitted, the full GraphQL response is returned.
     *
     * For example if the result is `{ a: [{b: "c"}]}`
     * you can set resultPath to `a[0].b` to retrieve only "c"
     */
    resultPath?: string;
  }

• Remove the "legacy" GitLabService.execute method and make the new GitLabService.fetchFromApi method accept the new GraphQLRequest.

• Drop the processResult callback.

  • this means that in some places we were returning GqlProject instead of GitLabProject and those places had to be updated
  • the getProjectsWithRepositoryInformation now can return undefined and so we had to add || [] to a few places that expected an array