Add Helmfile autodiscovery crawler

[olblak]

Signed-off-by: Olblak me@olblak.com

Fix #409

This pullrquest add the helmfile autodiscovery crawler.
By default it searches for all files matching [".yaml", ".yml"] if the crawler identify the following pattern in the file

repositories:
 - ...
releases:
 - ...

So it assumes that the repository used by a release is defined in the same file.

Test

To test this pull request, you can run the following commands:

# Unit Test
cd pkg/plugins/autodiscovery/helmfile
go test

## End to End test
go build -o bin/updatecli .
./bin/updatecli diff --config e2e/updatecli.d/warning.d/autodiscovery/helmfile --experimental --debug

Additional Information

Tradeoff

In order to be detected by Updatecli helmfile releases requires the following rules

1. A release and its repository must be located in the same file
2. A version must be specified for a release

Potential improvement

[olblak]

I am still missing UT to catch edgecases but at least it's already working and can be tested