Closes CH-157

Added support for a django-ninja template when using harness-application and harness-generate. Also refactored the application build process into a more structured process of builder components.

To test try generating applications using harness-application -t django-ninja and also using harness-generate servers for that app to see the generates servers and openapi schema.

...

Sanity checks:

[x] The pull request is explicitly linked to the relevant issue(s)
[x] 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

MetaCell / cloud-harness