Adapt relayer to work with dynamic lanes

[svyatonik]

Dynamic lanes are being added in #2213. There are no critical changes from relayer point of view, but its behavior can be improved. Like:

• no need to do anything with the lane if lane is missing from the storage (at any side of the bridge);
• no need to do anything unless the lane is in Opened/Closing state.

Some future PRs (like queue state propagation and coordination protocol) will add more work for relayers, so I'm gonna track this additional non-essential tasks in a separate PRs like that one