This is a late follow-up to lablup/backend.ai-webui#314.

Currently, the image label ai.backend.resource.min.mem is interpreted as the main memory size, excluding the shared memory size.However, the web UI's resource configuration automatically sets the shared memory size ($S$) to 64 MiB for the main memory sizes ($M$) less than 4 GiB, while our scheduler allocates the sum of the main memory size and the shared memory size ($M+S$).

This makes a confusion when allocating the least amount of memory $M+S = 256\ \mathrm{MiB}$, for instance, because it epic-fails as the web UI sends $M = 192\ \mathrm{MiB}$ and $S = 64\ \mathrm{MiB}$, while the manager's enqueue-session API handler compares the image label ai.backend.resource.min.mem with $M$ only and requires $M \ge 256\ \mathrm{MiB}$.

We are going to update the web UI to hide the detailed shared memory configuration for most use cases, and the memory resource slider will expose $M+S$ with auto-configured $S$ depending on the value of $M + S$.

To better support the above web UI update, let's change the enqueue-session API handler to:

• Compare ai.backend.resource.min.mem with $M+S$ instead of $M$.

• Raise an explicit input validation error if $S > M$, to prevent situations like $M = 0$ wihle $S = 1\ \mathrm{GiB}$.
  The Client SDK and CLI should still expose the raw configurations as the options. So, let's:

• Update the CLI's help texts to be explicitly consistent with the above changes.