Extra containers definition support: init and sidecars

[filippomc]

Closes CH-85

Implemented solution

Added init and sidecar containers as part of the deployment (extraContainers)

Example:

harness:
  ...
  deployment:
    ...
    extraContainers:
      init-print:
        auto: true
        initContainer: true
        commands: ["sh", "-c", "echo Initializing"]
        shareVolume: false
      sidecar-print:
        auto: true
        initContainer: false
        commands: ["sh", "-c", "while true; do echo Sidecar running at $(date); sleep 60; done"]
        shareVolume: false

How to test this PR

Implemented as part of samples application. Can check the online deployment or deploy it locally and check the pods.

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

[filippomc]

default django migration