The change introduces new entity `manager` which replaces
`watchdog`, decouples requestHandler and groups. Manager
supposed to control life cycle of groups, rules and
config reloads.
Groups export an ID method which returns a hash
from filename and group name. ID supposed to be unique
identifier across all loaded groups.
Some tests were added to improve coverage.
Bug with wrong annotation value if $value is used in
templates after metrics being restored fixed.
Notifier interface was extended to accept context.
New set of metrics was introduced for config reload.
* app/vmalert: restore alerts state from datasource metrics
Vmalert will restore alerts state for rules that have `rule.For` > 0 from previously written timeseries via `remotewrite.url` flag.
* app/vmalert: mention remotewerite and remoteread configuration in README
