Add custom grafana dashboards

closes #59 (closed)

Adds support for adding in custom grafana dashboards and removes GPT dashboards.

This is also removing the GTP dashboards and allowing them to be passed in as custom dashboards, as per #58 (closed), with the below additions to the inventory.

Inventory:

vars.yml

monitor_custom_dashboards: [{ name: 'gpt', display_name: 'GitLab Performance Tool', path: "{{ inventory_dir | default(ansible_inventory_sources[0], true) }}/../files/grafana/gpt" }]