Add parameter to specify image tag name

[tomuben]

Background

currently we use a hard coded name for the image tag of the docker container, consisting of flavor name and sha.
We would like to upload docker images for each release (see exasol/script-languages-release#56)
For that we need to overwrite the tag name with a a name from the command line.

Acceptance Criteria

The docker image tag name should be customizable, and the result should be $PARAM_NAME+FLAVOR_NAME

The parameter should be available for

1. build
2. run-db-test
3. save
4. push
5. export
6. upload