This commit updates the API to pass the MemoryMaxMB field, and the CLI to show
the max set for the task.
Also, start parsing the MemoryMaxMB in hcl2, as it's set by tags.
A sample CLI output; note the additional `Max: ` for "task":
```
$ nomad alloc status 96fbeb0b
ID = 96fbeb0b-a0b3-aa95-62bf-b8a39492fd5c
[...]
Task "cgroup-fetcher" is "running"
Task Resources
CPU Memory Disk Addresses
0/500 MHz 32 MiB/20 MiB 300 MiB
Task Events:
[...]
Task "task" is "running"
Task Resources
CPU Memory Disk Addresses
0/500 MHz 176 KiB/20 MiB 300 MiB
Max: 30 MiB
Task Events:
[...]
```
