Implement `RefillMetabase` method to `shardconfig.Config` type which reads
`refill_metabase` config value. Pass the result to `WithRefillMetabase`
option.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Add `size_limit` config value to write-cache section. Add `SizeLimit` method
of `writecache.Config` type. Pass its value to `WithMaxCacheSize` option on
app construction.
Reflect config update in examples. Cover new value in unit test.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Changes:
* replace `iotuil` elements with the ones from `os` package;
* replace `os.Filemode` with `fs.FileMode`;
* use `signal.NotifyContext` instead of `NewGracefulContext` (removed).
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
