For code review

Updated objectstore to use less memory

See merge request datastrophe/microservices-backbone/query-service!32

Merge branch '375-cache-query-result' of git.science.uu.nl:datastrophe/microservices-backbone/query-service into 375-cache-query-result

# Conflicts:
#   go.mod
#   go.sum

Added status messages for queries in progress.

Moved the query caching code underneath the result publish code, as the
caching was increasing the time before the result was returned.

Added prometheus metrics tracking

See merge request datastrophe/microservices-backbone/query-service!31

Also added the Minio environment variables to the Kubernetes deployment.

Added MessageStruct to describe outgoing messages

See merge request datastrophe/microservices-backbone/query-service!29

Re-ordered operations in the method as well. Empty database check now
happens before query translation.

Result message now also uses the entity.MessageStruct. This will have to
be changed in the frontend before merging.

Replaced all maps in the handleMessage method with the MessageStruct,
except for the final result, as this one uses the key 'values', where
the rest use the key 'value'. Once this has been changed in the frontend
it will be updated in the backend as well.

Externalize packages

See merge request datastrophe/microservices-backbone/query-service!28