Git files generator: add support for YAML files

[jgwest]

The initial Git files generator support has merged, but it currently only supports processing JSON files from a git repository.

The ApplicationSet design design doc notes that "referenced files would contain a json/yaml list of arbitrary structured objects", and thus I have opened this issue to track adding support for YAML files within git.

If/when this is implemented, search through the (markdown) docs for references to JSON, and update them to JSON/YAML.

[marcozov]

Sorry if this is not relevant, but: should this also support a way to pass parameters/values from this file, as a unique YAML block?
This is the use case that I have in mind: https://argocd-applicationset.readthedocs.io/en/stable/Use-Cases/#use-case-self-service-of-argo-cd-applications-on-multitenant-clusters . What if I, as administrator, want to provide users the possibility of generating N applications in a specific project (that I fix, just like it's shown in the example) with their own values?

[andrejpetras]

Hi, I created PoC for my case.

https://github.com/lorislab/applicationset/tree/yaml

I put a short description in the README file.
The generator in the ApplicationSet is the git generator which will check if file ends with .yaml
Before the template is generated from the yaml file it will be merged with global.yml file if exists.
Template parameters are [root key] = string value of the merged yaml.

Source code: https://github.com/lorislab/applicationset/blob/yaml/pkg/generators/git.go#L221

[jgwest]

As mentioned on 173, I think this issue should first stick to implementing the YAML parsing functionality consistent with the JSON parsing functionality, before we add new changes on top as proposed in the lorislab yaml branch, eg per-directory values (the global.yml), changes to how file values are flattened, and addition of new path and path.basename parameters.

[teejaded]

JSON is a subset of YAML. Pretty sure we can just switch to a YAML parser. This passes the go-tests.

#211