Create template for upgrade pull requests

[dylanschultzie]

@JeremyParish69 I'm going to create a template so that you don't have to keep going into these PRs and telling me (and others) to add other things. The plan is:

1. Normalize PR name to [upgrade] {network} {version}
2. Add estimated time to be filled in for the PR body:

Estimated Upgrade Time: 

3. Add a comment block for the PR that shows and example of (new) major version increases.

One problem I see is this really only works for consensus-breaking upgrades/gov-prop upgrades. Non consensus-breaking upgrades don't require all of this.