[drone-runner-ssh, drone-runner-exec] Add support for (V2) environment extensions

[mach6]

Background

As is stands now, drone-runner-ssh and drone-runner-exec do not support environment extensions.

Proposal

The proposal is to update these runners to more recent versions of drone-go and runner-go, which include the support for the V2 version of the environment extension spec, then add support for environment extensions.

Pending Changes

Please note: If this proposal is accepted, I have made the necessary changes to both runners and have tested on linux-amd64. All changes were modeled after the current code in drone-runner-docker.

I will also open PRs and link them to this proposal.

Help Needed

I could use some help verifying the changes on these platforms, which I do not have access to.

drone-runner-ssh

• [ ] linux-arm
• [ ] linux-arm64
• [x] linux-amd64

drone-runner-exec

• [ ] linux-arm
• [ ] linux-arm64
• [ ] linux-386
• [x] linux-amd64
• [ ] windows-386
• [x] windows-amd64
• [x] darwin-amd64
• [ ] freebsd-amd64
• [ ] freebsd-arm
• [ ] freebsd-386
• [ ] netbsd-amd64
• [ ] netbsd-arm
• [ ] openbsd-amd64
• [ ] openbsd-arm
• [ ] openbsd-386
• [ ] dragonfly-amd64
• [ ] solaris-amd64

Note: A check mark denotes that it has been spot tested.

[mach6]

@tphoney @bradrydzewski Anything you need from me on this proposal and/or the open PRs?