MGS: Add support for new component details variants: `LastPostCode` and `GpioToggleCount`

[jgallagher]

#9354 pulls in a new gateway-messages that added a couple new kinds of ComponentDetails messages, and (for ease of backporting to a release branch) MGS will return a 400 if those new kinds are requested. We have no control plane callers of these, so there's not currently a way to actually see that 400 (other than manually curling the endpoint or similar). However, eventually we will want to ask for these - we should update the MGS API to be aware of these new variants.