Normalize Makefile to ci-mgmt

[iwahbe]

Hello!

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Issue details

pulumi-aws currently uses a bespoke Makefile. To simplify use and allow automated upgrades, we should convert to a Makefile generated by ci-mgmt.

This involves switching upstream to a patch managed system, as opposed to a fork managed one. The important part of this PR is that the upgrade process looks just like a normal bridged provider, and that we can automate with upgrade-provider.

To accommodate for the special behavior still needed by pulumi-aws (specifically running upstream-tools), we can add a hook system to the generated Makefile and import a local Makefile (if it exists). The goal here is to keep any pulumi-aws specific Make targets in the pulumi-aws repo without breaking the build.

Related: pulumi/ci-mgmt#518 disabled Makefile generation for pulumi-aws. As part of closing this issue, we should undo this commit.

Like #2708, the PR that closes this issue will need to be duplicated in pulumi-aws and ci-mgmt.

Affected area/feature

The Makefile.

[guineveresaenger]

Closing as done via both linked PRs.