Tune facia-rendering And tag-page-rendering

[JamieB-gu]

Previously we had a single stack for rendering fronts and tag pages: facia-rendering. In #11421 we created a new stack, tag-page-rendering, and sent all tag page traffic to that. We did not change the size (number of instances) or scaling policy of the facia-rendering stack, and we created the new tag-page-rendering stack using exactly the same rules.

As a result, both stacks now have different traffic patterns to what those rules were optimised for. facia-rendering now serves only fronts traffic, and tag-page-rendering serves only tag page traffic.

Therefore we should tune the size and the scaling policy of both stacks to suit their new traffic patterns. This will likely at least mean reducing the minimum number of instances for both.

[alinaboghiu]

We should pull this into our next health sprint in June