* app/vmalert: add retries to remotewrite
Remotewrite pkg now does limited number of retries if write request failed.
This suppose to make vmalert state persisting more reliable.
New metrics were added to remotewrite in order to track rows/bytes sent/dropped.
defaultFlushInterval was increased from 1s to 5s for sanity reasons.
* fix
* wip
* wip
* wip
* fix bits alignment bug for 32-bit systems
* fix mistakenly dropped field