Linear update flow + UpdateSelectors

[l0kix2]

Linear flow

Administators should have more control over YTsaurus cluster update. Currently, components are being updated simultaneously (though some dependencies described in code) and it is hard to understand what component needs attention if some issue arises and update is stuck. To achieve that it suggested to implement linear update flow, when no more than one component is being updated at a time. It is addressed in "Linear update flow" issue #115.

Update selectors

Sometimes it preferable to update only subset of YTsaurus components or even only one component. To address this issue experimental updateSelector field was introduced some time ago. Though we had some issues using it.
At first it has only couple sets of components to update (master only, stateful only, stateless only, tablets only, exec nodes only), but it is required to have more granular set of selector when it is possible to update one particular component or some set of components filtered by type or some combination of it.
Also statelessOnly includes dataNodes which is confusing.
Moreover there is a Reconfiguration status, which happens when something needs to be created, which is considered "safe" action, but recently we've discovered that it may lead to sts update, which can lead to pods re-creation. It will be good to either respect updateSelector in the Reconfiguration or maybe merge Reconfiguration flow with the Updating flow for thing to be simpler.

Those issues are addressed in

• "UpdateSelector needs to be decoupled" UpdateSelector needs to be decoupled #325 and
• "Reconfiguration state should respect updateSelector" Reconfiguration state should respect updateSelector #353