[receiver/vcenter] Updates vcenter.cluster.memory.used Metric Confi…

…g With Warning (#32807)

**Description:** <Describe what has changed.>
This metric is not actually implemented. Adding a warning for now if a
user has it configured in some way to let them know that it'll be going
away soon.

**Link to tracking Issue:** <Issue number if applicable>
#32805 

**Testing:** <Describe what testing was performed and which tests were
added.>
Unit/integration tests updated and tested. Local environment tested.

**Documentation:** <Describe the documentation added.>
N/A

.chloggen/fix_vcenter-cluster-unused-metric-warning.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: "Adds warning to `vcenter.cluster.memory.used` metric if configured about its future removal"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32805]
+
+# (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: [user]

receiver/vcenterreceiver/metadata.yaml

@@ -149,6 +149,8 @@ metrics:
       value_type: int
       aggregation_temporality: cumulative
     attributes: []
+    warnings:
+      if_configured: this metric is unimplemented & will be removed starting in release v0.101.0
   vcenter.cluster.vm.count:
     enabled: true
     description: The number of virtual machines in the cluster.