Add memory limits configuration into walking skeleton flow

[garagatyi]

Description

Now we don't have memory limits in the walking skeleton. This leads us to a situation when all the sidecars irrespective of their RAM usage a configured with the default machine RAM limit - 1GB, for example.
We can improve this situation by implementing the next steps:

• 1. Add a field in the sidecar config to allow the author of the plugin to configure memory limit.
  This would address sidecars with still RAM consumption that doesn't depend on the workspace projects size.
• 2. Add a property to Che master that would configure the default memory limit for sidecars with small enough value, such as 128MB.
  This would address a case when the plugin author didn't set memory limit and the default Che machine limit is too high for a sidecar.
• 3. Allow a user to specify workspace config attribute that would override sidecar memory limit from sidecar definition or default sidecar memory limit.
  This would address a situation with JDT.LS like sidecars when usage of RAM depends on the workspace projects size and not really possible to be predicted by the author of a plugin.

Reproduction Steps

OS and version:

Diagnostics:

[garagatyi]

@skabashnyuk @l0rd @benoitf I'm going to add a field memory-limit to the Container object of the plugin from the WS.NEXT model. It will support kubernetes notion of memory limits, such as: E, P, T, G, M, K, Ei, Pi, Ti, Gi, Mi, Ki - 10Gi, 300Ki.
If you have ideas what can be implemented in a better way, please, comment.

[garagatyi]

Closing as fixed