Adding Docker login to Github bulid-and-push job

[danjbh]

what & why?

• Adding Docker login step to build-and-push job since it's currently borked

references

docker/build-push-action#88 (comment)

[danjbh]

Alright @osterman , it took a bit of tinkering to get the rest of the steps sorted out, but it's in a working state at this point, as far as I can tell at least.

Definitely have a look at the Prep step in bash logic to see if you think we need any tweaks there. I tried to mirror what I think how the previous tagging was working at least.

Let me know!