First 'bwc-ui' dev package is not built during the release

[arm4b]

st2cd.st2_prep_dev workflow which is part of https://github.com/StackStorm/discussions/wiki/Release-Process#process-for-major-release doesn't trigger a bwc-ui package generation, which means that first dev package is not built and that, of course, fails in installer (you should trigger the build manually in CircleCI bwc-ui for now).

Not exactly the same, but related problem and technical debt is that bwc-ui package is a replacement for st2web so every time we change the st2web code we should re-build bwc-ui package as well. The solution is to make bwc-ui a module/extension for web ui, like st2flow and not a replacement.

[bigmstone]

Related: extremenetworks/ewc#3