Single unified Template holding multiple item types (SNMP, HTTP/API, Script) per device — not separate Monitor + OID templates

[Kirubananthan-Kuppan]

Is your feature request related to a problem? Please describe.
Today, configuring one device type requires two disconnected templates:
Monitor Template (alert rules) and OID Collection Template (SNMP data only).
There's no way to also pull data from an HTTP/API source (e.g., Meraki
dashboard API for WAN status, serial number, manufacturer) or a Script check,
attach it to the same device, and use it for alerting — because only SNMP
OIDs have a collection mechanism at all.

Describe the solution you'd like
One template (e.g., "Unit Router Template") that works like a Zabbix Host's
Item list: inside it, add any number of "collectors," each independently
typed:

• SNMP OID (existing OID Collection Template logic, folded in here)
• HTTP/API (endpoint, auth, response field mapping)
• Script/Custom check
• (any other monitor type already supported elsewhere in OneUptime)

Then, for any device linked to this one template:

1. All collected values become selectable Monitor Criteria — trigger
   alerts on any item, from any source, same as today's OID criteria.
2. All collected values show on the Device Details page — e.g., WAN1
   status, Serial Number, CPU%, fetched from whichever source, displayed
   together on one device.
3. All collected values appear in Inventory/Custom Fields — so device
   listings can show and filter on this data too.

Auto Import Rules link ONE template per device (not two), and that template
carries everything: what to collect (any source) and what to alert on.

Additional context
This replaces the earlier, narrower "OID Collection Template" and "Monitor
Template" as two separate systems — the OID logic already built should
become one item type inside this unified template, not a parallel structure.

Deployment Type: Self hosted
Version: OneUptime 12.0.30