Improvements around service scalability

[valeksiev]

Describe the background of your pull request

• move batch size to env var with a default of 20
• base winston log level on the LOGGING_LEVEL variable and ensure it is lowercase
• auto ack messages when received

Additional context

Fixes: #38

Governance

• Documentation is added
• Test cases are added or updated

By submitting this pull request I confirm that:

• I've read the contributing document https://github.com/alkem-io/.github/blob/master/CONTRIBUTING.md.
• I've read and understand the Code of Conduct https://github.com/alkem-io/.github/blob/master/CODE_OF_CONDUCT.md.
• I understand that any contributions or suggestions I made may make it into the actual code. I've read the License
  https://github.com/alkem-io/Coordination/blob/master/LICENSE.
• I understand that submitting the pull request requires agreeing to and signing the contributor license agreement.

[hero101]

Just a general comment - with message being auto ack, the service can still hang, at least we will know it's not because of message order