Allow build container to accept Makefile parameters

[korydraughn]

This would allow developers to build the builder image one time and then generate documentation for different github accounts and commits at any time.

This removes the need for developers to modify the Makefile.

[alanking]

Do we need to cherry-pick to 4-2-stable?

[korydraughn]

I don't think so. The 4-2-stable branch is in its final stretch and I don't feel we need to devote time to porting these features to it.

Thoughts?

[trel]

Yes, let's leave 4-2-stable docs machinery as is - we'll just update the .md that gets shipped with any additional 4.2.x releases.

[alanking]

Sounds good