Create "released_plugins" branch.

# Refactor

Create `released_plugins` branch that contains the changes for released plugins. Document plugin release procedure in confluence.

# Tasks

- [ ] ~Create a branch that would have the released plugin codebase~ (Moved to separate repos)
- [ ] Document the procedure of plugin release. Try to answer the questions "how to build, test and release a plugin?", "what branch I need to make and where do I merge it", etc.