feat: add support for alarms (#2600)

Adds support for vSphere alarms resource and data source.

Ref: #1312

Author: emriver

docs/data-sources/alarm.md

@@ -0,0 +1,47 @@
+---
+subcategory: "Inventory"
+page_title: "VMware vSphere: vsphere_alarm"
+sidebar_current: "docs-vsphere-data-source-alarm"
+description: |-
+  Provides a vSphere alarm data source. Returns attributes of a
+  vSphere alarm.
+---
+
+# vsphere_compute_cluster_host_group
+
+The `vsphere_alarm` data source can be used to retrieve the property of a given alarm.
+
+## Example Usage
+
+```hcl
+data "vsphere_datacenter" "datacenter" {
+  name = "dc-01"
+}
+
+data "vsphere_alarm" "alarm" {
+  entity_type = "Datacenter"
+  entity_id   = data.vsphere_datacenter.dc.id
+  name        = "example"
+}
+```
+
+## Argument Reference
+
+The following arguments are supported:
+
+* `name` - (Required) The name of the host group.
+* `entity_id` - (Required) The [managed object reference ID][docs-about-morefs] of the entity the alarm will be created in.
+* `entity_type` - (Required) The type of the entity the alarm will be created in.
+
+## Attribute Reference
+* `id`: The [managed object reference ID][docs-about-morefs] of the alarm.
+* `enabled` - Whether or not the alarm is enabled.
+* `expression_operator` - The logical link between expressions.
+* `event_expression` - The event expressions of the alarm.
+* `metric_expression` - The metric expressions of the alarm.
+* `state_expression` - The state expressions of the alarm.
+* `advanced_action` - The advanced actions of the alarm.
+* `email_action` - The email alarm actions of the alarm.
+* `snmp_action` - The snmp alarm actions of the alarm.
+
+[docs-about-morefs]: /docs/providers/vsphere/index.html#use-of-managed-object-references-by-the-vsphere-provider

docs/resources/alarm.md

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+---
+subcategory: "Inventory"
+page_title: "VMware vSphere: vsphere_alarm"
+sidebar_current: "docs-vsphere-resource-inventory-alarm"
+description: |-
+  Provides a VMware vSphere alarm resource. This can be used deployed on all kinds of vSphere inventory objects.
+---
+
+# vsphere_alarm
+
+Provides a VMware vSphere alarm resource. This can be used deployed on all kinds of vSphere inventory objects.
+
+## Example Usages
+
+**Create warning alarm with an email action on a datacenter when on a host is disconnected:**
+
+```hcl
+resource "vsphere_alarm" "host_disconnected_warning" {
+  name        = "Host disconnected"
+  description = "Triggers a warning when a host is disconnected"
+  entity_type = "Datacenter"
+  entity_id   = data.vsphere_datacenter.datacenter.id
+
+  state_expression {
+    operator    = "isEqual"
+    state_path  = "runtime.connectionState"
+    object_type = "HostSystem"
+    yellow      = "disconnected"
+  }
+
+  email_action {
+    to          = "foo@example.com"
+    subject     = "Host disconnected"
+    start_state = "green"
+    final_state = "yellow"
+  }
+}
+```
+
+**Create critical alarm when a host CPU usage is above 95% for 5min:**
+
+```hcl
+resource "vsphere_alarm" "host_disconnected_warning" {
+  name        = "Host CPU usage"
+  description = "Triggers a critical when a host CPU usage is too high"
+  entity_type = "Datacenter"
+  entity_id   = data.vsphere_datacenter.datacenter.id
+
+  metric_expression {
+    metric_counter_id = 2 # hosted counter ID for CPU usage
+    operator          = "isAbove"
+    object_type       = "HostSystem"
+    red               = 9500
+    red_interval      = 300
+  }
+}
+```
+
+**Create alarm to set a host in maintenance when a lacp down event occurs, and remove the maintenance when the lacp is up again:**
+
+```hcl
+resource "vsphere_alarm" "lacp_down_on_host" {
+  name        = "LACP down on host"
+  description = "Set the host is maintenance if lacp goes down"
+  entity_type = "Datacenter"
+  entity_id   = data.vsphere_datacenter.datacenter.id
+
+  # alert
+  event_expression {
+    event_type_id = "esx.problem.net.lacp.lag.transition.down"
+    object_type   = "HostSystem"
+    status        = "red"
+  }
+
+  # recovery
+  event_expression {
+    event_type_id = "esx.problem.net.lacp.lag.transition.up"
+    object_type   = "HostSystem"
+    status        = "green"
+  }
+
+  # enter maintenance mode if alert is triggered
+  advanced_action {
+    start_state = "green"
+    final_state = "red"
+    name        = "EnterMaintenanceMode_Task"
+  }
+
+  # remove maintenance mode on alert² recovery
+  advanced_action {
+    start_state = "red"
+    final_state = "green"
+    name        = "ExitMaintenanceMode_Task"
+  }
+}
+```
+
+## Argument Reference
+
+The following arguments are supported:
+
+* `name` - (Required) The name of the alarm. This name needs to be unique
+  within the vCenter. Forces a new resource if changed.
+* `description` - (Optional) The alarm description.
+* `enabled` - (Optional) Whether or not the alarm is enabled.
+* `entity_id` - (Required) The [managed object reference ID][docs-about-morefs] of the entity the alarm will be created in.
+* `entity_type` - (Required) The type of the entity the alarm will be created in.
+* `expression_operator` - (Optional) The logical link between expressions.
+* `event_expression` - (Optional) Alarm trigger expressions based on events.
+* `metric_expression` - (Optional) Alarm trigger expressions based on metric values.
+* `state_expression` - (Optional) Alarm trigger expressions based on object state changes.
+* `advanced_action` - (Optional) Advanced alarm action to trigger depending on the alarm state, such as entering maintenance mode.
+* `email_action` - (Optional) Email alarm action to trigger depending on the alarm state.
+* `snmp_action` - (Optional) Snmp alarm action to trigger depending on the alarm state.
+
+## Attribute Reference
+
+* `id` - The ID of the alarm.
+
+## Importing
+
+Importing vSphere alarm is not managed.