Internally in `emqx_resource_manager`, there seems to be many points where the
`gen_statem` states are conflated with resource status, since their names coincide. While
that works for now, introducing a new `gen_statem` state, an internal state, shouldn't
necessarily imply a new, externally facing resource status.
Here we also introduce the usage of some macros to avoid the pitfalls of making a typo in
a state/status name.
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