Variables: Allow fetching disabled items for Item type variable (#2109)

This PR adds support for showing disabled items when using the `Item`
type template variable. Similar to how we support disabled items today
in our query editor:


<img width="435" height="254" alt="Screenshot 2025-10-21 at 9 00 11 AM"
src="https://github.com/user-attachments/assets/832537c8-84c3-45fe-a85d-b16c8e15f759"
/>

In this example, the host contains a disabled item `CPU iowait time`

<img width="1763" height="46" alt="Screenshot 2025-10-21 at 9 02 08 AM"
src="https://github.com/user-attachments/assets/85419e88-280d-4dce-baee-bf403e1de05d"
/>

Which we can now show and hide from the variable in Grafana:



https://github.com/user-attachments/assets/eca9327e-40a6-4852-92e9-71ff1ad9ea32

I also removed some deprecated types and packages :)!
Fixes: #2025

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

.changeset/nasty-webs-repeat.md

@@ -0,0 +1,5 @@
+---
+'grafana-zabbix': minor
+---
+
+Add support for disabled items in Item variable type