Add fix instructions to incorrect origin message.

[fredemmott]

• move stuff around so that --dry-run can be used to test this
• Use --push URLs so support pulling from https and pushing with ssh. This lets you pull/rebase etc without access to an SSH key, which is convenient if it's stored on a yubikey for example
• Provide fix instructions

Test Plan:

$ git remote set-url --push origin https://example.com
$ bin/promote-nightly-to-release 2021.11.18 4.136 --dry-run --force
----------------
--- Versions ---
----------------
Nightly build:
  2021.11.18
Previous version:
  4.135
Tagging version:
  4.136
----------------
[WARNING - FORCED] Run from master branch.
[WARNING - FORCED] Uncommitted changes.
[WARNING - FORCED] Git origin push URL is unsupported:
  - Current value: https://example.com
  - Required value: git@github.com:hhvm/packaging.git
  - Fix:
     git remote set-url --push origin git@github.com:hhvm/packaging.git
Dry run - exiting.
$ git remote set-url --push origin git@github.com:hhvm/packaging.git
$ bin/promote-nightly-to-release --dry-run 2021.11.18 4.136 --force
----------------
--- Versions ---
----------------
Nightly build:
  2021.11.18
Previous version:
  4.135
Tagging version:
  4.136
----------------
[WARNING - FORCED] Run from master branch.
[WARNING - FORCED] Uncommitted changes.
Dry run - exiting.