Node view should include available values

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Checklist:

* [x] I've searched in the docs and FAQ for my answer: https://bit.ly/argocd-faq.
* [x] I've included steps to reproduce the bug.
* [x] I've pasted the output of `argocd version`.

**Describe the bug**

The graphs show requests, neighbors, and capacity. In theory a human can do the math to calculate availability, but in practice computers are much better

**To Reproduce**

1. Visit https://cd.apps.argoproj.io/applications/argo-cd?view=pods
2. Group by node
3. Hover over memory or cpu for a node

**Expected behavior**

Calculate available in addition to showing used and capacity

**Screenshots**


**Version**

```shell
{
"Version": "v1.9.0+bb15a49",
"BuildDate": "2021-02-06T00:55:32Z",
"GitCommit": "bb15a4996e327fb27ad91f3f6fa24f831f7754e0",
"GitTreeState": "clean",
"GoVersion": "go1.14.12",
"Compiler": "gc",
"Platform": "linux/amd64",
"KsonnetVersion": "v0.13.1",
"KustomizeVersion": "v3.8.1 2020-07-16T00:58:46Z",
"HelmVersion": "v3.5.1+g32c2223",
"KubectlVersion": "v0.20.1",
"JsonnetVersion": "v0.17.0"
}
```

**Logs**

```
Paste any relevant application logs here.
```

Reproduce the issue in the linked Argo CD application by opening the pods view, grouping by node, and hovering over memory or CPU. Trace the node view graph that displays requests, neighbors, and capacity; done means the view also shows the calculated available value.

Written by the indexing model from the issue text.