Feature/592 Avoid doing the same repeated build in the dev/test pipelines

[filippomc]

Closes #592
Closes #679 (minor change)

Implemented solution: Changed the way that tags have been assigned to applications. Now tags are created from
an hashing of the content and this is used to check if the image already exists in the registry.
Builds for images that already exist are skipped on Codefresh

How to test this PR: run twice the same pipeline to see that builds are not repeated.

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)
• From the issue and the current 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.)
• All the automated test checks are passing
• All the linked issues are included in one milestone
• All the linked issues are in the Review/QA column of the board
• 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

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 as the way images are tagged changed; also images that rely on data external to the cloned data won't be updated as previously (same was due to the codefresh cache btw)

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