Heroes 5.5 WarGame Edition - Tactical Edition.

What kind of production buildings can be built in Heroes near an enemy?

You can't build anything, but the closest analogue is capturing dwellings along the way to or near a city and "boosting" the strength of your army in this way.
I gave examples from Starcraft. Therefore, for example, I can't yet come up with an analogue of a rush through aggressive buildings. Theoretically, this could be occupying passages and garrisons, cutting off the enemy's troops from the city, followed by strengthening the army and taking the city, but in practice, it is unknown how this will play out at all. On paper, it looks one way, but in reality, it may turn out to be much simpler.

By the way, here's an idea for the Orcs - to receive useful bonuses for sacrificing goblins.

I don't know, I don't really want to introduce rituals for the sake of rituals. If we are talking about a ritual that creates a fundamentally new tier or set of units, then we can consider it. For example, a one-time significant boost to turn order or an instant summoning of reinforcements - this is a fundamental boost that qualitatively changes the situation, but passive bonuses to attack, defense, etc. - no.
And if there is a ritual by default for all Orcs, then this restricts the rights of those players who will not build goblins. In its current form (according to the schemes I proposed), building is good because no unit is mandatory.
Even a Necromancer can manage without skeletons, playing through magical builds with spirits and liches with zombies.