Optional image building

[filippomc]

Closes CH-169
Fixes CH-134

Implemented solution

Changed the scripts to check whether the harness.deployment.image is set and ignore the build in that case, even if a dockerfile is present.

On the side, removed the build for the nfs-server using this implemented strategy, as that build currently fails and is not necessary.

How to test this PR

Set harness.deployment.image to something and verify that skaffold and codefresh script do not contain that build, and the image is correctly set in values.yaml
The new functionality behaviours are fully covered in unit tests.

Sanity checks:

• The pull request is explicitly linked to the relevant issue(s)
• The issue is well described: clearly states the problem and the general proposed solution(s)
• In this PR it is explicitly stated how to test the current change
• The labels in the issue set the scope and the type of issue (bug, feature, etc.)
• The relevant components are indicated in the issue (if any)
• All the automated test checks are passing
• All the linked issues are included in one Sprint
• All the linked issues are in the Review state
• All the linked issues are assigned

Breaking changes (select one):

• The present changes do not change the preexisting api in any way
• This PR and the issue are tagged as a breaking-change and the migration procedure is well described above

Possible deployment updates issues (select one):

• There is no reason why deployments based on CloudHarness may break after the current update
• This PR and the issue are tagged as alert:deployment

Test coverage (select one):

• Tests for the relevant cases are included in this pr
• The changes included in this pr are out of the current test coverage scope

Documentation (select one):

• The documentation has been updated to match the current changes
• The changes included in this PR are out of the current documentation scope

Nice to have (if relevant):

• Screenshots of the changes
• Explanatory video/animated gif