feat(scheduling): add volume group capacity tracking

[iyashu]

Why is this PR required? What issue does it fix?:
With k8s version >= 1.19, there is feature(alpha stage) added where the kube-scheduler gets influenced by storage capacity available on nodes during filtering stage. Without CSIStorageCapacity tracking, a pod with a volume that uses delayed binding may get scheduled multiple times, but might always land on the same node unless there are multiple nodes with equal priority. More details are mentioned in KEP 1472 & external provisioner documentation.

What this PR does?:
We introduced a new custom resource called LVMNode recording all the available vgs and its corresponding attributes in each node. Openebs node plugin running on each node will periodically scan vgs and reconcile LVMNode resource. At controller side, we've implemented CSI GetCapacity method called by k8s external-provisioner for creating/updating CSIStorageCapacity objects which in turn used by kube-scheduler for each node topology. K8s external-provisioner calls GetCapacity for every combination of storage class and node topology segments (individual nodes in our case). So, volume group configured in storage class is also a part of args in GetCapacity method. In case, there are multiple volume group (with multi pool support) available on nodes, we choose the volume group having maximum free capacity & its name matching to volgroup parameter of the GetCapacity call.

Does this PR require any upgrade changes?:
No

If the changes in this PR are manually verified, list down the scenarios covered::
Consider a kubernetes cluster having 5 worker nodes (besides master ones) each having a storage capacity of size 32 Gi. Create a stateful set cluster say sts-a of size 4 each requesting storage capacity(pvc) of size 20Gi. Now create another stateful set cluster say sts-b of size 1 again requesting storage capacity(pvc) of size 20Gi. We'll see that pod in sts-b will be scheduled (by kube-scheduler) on right node having enough capacity.

Any additional information for your reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• Fixes #
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

[codecov-io]

Codecov Report

Merging #21 (ef941f5) into master (311e12b) will decrease coverage by 0.11%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master     #21      +/-   ##
=========================================
- Coverage    1.20%   1.08%   -0.12%     
=========================================
  Files          11      11              
  Lines         831     920      +89     
=========================================
  Hits           10      10              
- Misses        821     910      +89     

Impacted Files	Coverage Δ
pkg/driver/agent.go	0.00% <0.00%> (ø)
pkg/driver/controller.go	0.63% <0.00%> (-0.15%)	⬇️

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[iyashu]

Gentle reminder @pawanpraka1 @akhilerm

[prateekpandey14]

we can start using v1 CRDs version ..v1beta going to be deprecated in k8s 1.22

[iyashu]

Yeah, I had initially configured the same, then saw that other crds (LVMSnapshot, LVMVolume etc) are using v1beta1. I think, we can take this up as part of separate pull request as it'll required changes to other crds as well.

[prateekpandey14]

We can start using the controller-gen verison v0.4.0 version which will basically generates the v1 CRD version by default.

[akhilerm]

LGTM

[prateekpandey14]

LGTM, some of the changes like CRDs version etc going to be fixed in upcoming PRs

[pawanpraka1]

@iyashu why do we need watcher for lvmnode object? does node daemonset need to take any action as per modification/updation of lvmnode object?