MM-14037 Ensure deprecated image proxy settings are read correctly (#10249)

model/config.go

@@ -278,9 +278,9 @@ type ServiceSettings struct {
 	ExperimentalEnableDefaultChannelLeaveJoinMessages *bool
 	ExperimentalGroupUnreadChannels                   *string
 	ExperimentalChannelOrganization                   *bool
-	DEPRECATED_DO_NOT_USE_ImageProxyType              *string `json:"ImageProxyType"`    // This field is deprecated and must not be used.
-	DEPRECATED_DO_NOT_USE_ImageProxyURL               *string `json:"ImageProxyURL"`     // This field is deprecated and must not be used.
-	DEPRECATED_DO_NOT_USE_ImageProxyOptions           *string `json:"ImageProxyOptions"` // This field is deprecated and must not be used.
+	DEPRECATED_DO_NOT_USE_ImageProxyType              *string `json:"ImageProxyType" mapstructure:"ImageProxyType"`       // This field is deprecated and must not be used.
+	DEPRECATED_DO_NOT_USE_ImageProxyURL               *string `json:"ImageProxyURL" mapstructure:"ImageProxyURL"`         // This field is deprecated and must not be used.
+	DEPRECATED_DO_NOT_USE_ImageProxyOptions           *string `json:"ImageProxyOptions" mapstructure:"ImageProxyOptions"` // This field is deprecated and must not be used.
 	EnableAPITeamDeletion                             *bool
 	ExperimentalEnableHardenedMode                    *bool
 	ExperimentalStrictCSRFEnforcement                 *bool