fix(metrics): announce sidecar injection capability (#776)

The operator was not announcing the TYPE_INSTANCE_SIDECAR_INJECTION
capability so the CNPG operator did not consider the plugin enabled
for instance pods. The instance manager never queried the plugin's
metrics endpoint, and the barman_cloud_cloudnative_pg_io_* metrics
were missing entirely.

This bug was masked when isWALArchiver was set to true in the plugin
configuration, because the backward compatibility code in CNPG would
mark the plugin as enabled as a side-effect. Users with isWALArchiver
set to false (or omitted) never saw the new metrics.

Closes #682 

Signed-off-by: Kenny Root <kenny@the-b.org>

Author: kruton

internal/cnpgi/operator/identity.go

@@ -62,6 +62,13 @@ func (i IdentityImplementation) GetPluginCapabilities(
 					},
 				},
 			},
+			{
+				Type: &identity.PluginCapability_Service_{
+					Service: &identity.PluginCapability_Service{
+						Type: identity.PluginCapability_Service_TYPE_INSTANCE_SIDECAR_INJECTION,
+					},
+				},
+			},
 		},
 	}, nil
 }