fix npe on some metrics for vcenter vms (open-telemetry#41701)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

I believe that this should be the only nullable field improperly
accessed within this file.

```go
// The ConfigInfo data object type encapsulates the configuration settings and
// virtual hardware for a virtual machine.
//
// This type holds all the information
// that is present in the .vmx configuration file for the virtual machine.
type VirtualMachineConfigInfo struct {
```

I'm thinking users may have created a machine and attached the vmdk to
it and thats may be the potential cause?

Either way this should resolve the NPE and shouldn't crash the collector
when we encounter these.

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes open-telemetry#41018

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#### Testing

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#### Documentation

Changelog

Author: schmikei

.chloggen/main.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: vcenterreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fixes a potential NPE during VM collection
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [41018]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/vcenterreceiver/processors.go

@@ -307,7 +307,7 @@ func (v *vcenterMetricScraper) buildVMMetrics(
 	}
 
 	groupInfo = &vmGroupInfo{poweredOff: 0, poweredOn: 0, suspended: 0, templates: 0}
-	if vm.Config.Template {
+	if vm.Config != nil && vm.Config.Template {
 		groupInfo.templates++
 	} else {
 		switch vm.Runtime.PowerState {