- allow to pass s3 writer host

fixed bug on stats when using s3 bypass

- fixed missing stats when bypassing pipeline

- avoid to set bypass mode when using reservoir sampling

- remove default mail from, allow to set from environment

- customizable write buffer, needed for:

- reservoir sampling write buffer

- json line files must finish with \n for allowing direct concatenation

- some minor bugfixing

- added some extra logs to s3 reader

- mail_from fix in SES mail notifier

group option not needed in kafka reader (avoid validation errors with…

… it)