Draft a proposal for the Upgrades & Dependency Management epic

**Describe the problem/challenge you have**
We have many use cases that we'd like to address related to Upgrades & Dependency Management (see #361) for kapp-controller.

**Describe the solution you'd like**
Following the [proposals process](https://github.com/vmware-tanzu/carvel/tree/develop/proposals), we'd like to gain alignment on what we're setting out to achieve with this epic.

**Anything else you would like to add:**

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