Draft: Add developer's guide

Information about project branching strategy, LTS process and release process as well as support cycle of the releases

Signed-off-by: Pavel Zhukov pavel.zhukov@huawei.com

assigned to @landgraf

@landgraf Doesn't this need a review from docs team?

@nawab it will but once we figure out new EF processes. That's why it's in Draft state

@landgraf Sure, thanks

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