fix(yaml,file) fail validation when the file does not exist

[dduportal]

This PR follows up #398 and adds a validation for the resources yaml and file.

It fails the validation if the specified file does not exist: it helps end user when they have a typo...

Example of output:

CONDITIONS:
===========

checkUsernameYaml
-----------------
ERROR: Validation error: the provided manifest configuration had the following validation errors:
Invalid spec for yaml resource: the file "toto;yaml" does not exist.

checkUsernameFile
-----------------
ERROR: Validation error: the provided manifest configuration had the following validation errors:
Invalid spec for yaml resource: the file "toto;yaml" does not exist.

Test

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

• Nominal case (non regression):

go build -o dist/updatecli && ./dist/updatecli --config ./examples/updatecli.generic/yaml.yaml diff && ./dist/updatecli --config ./examples/updatecli.generic/file.yaml diff

• Check the new validation failure:

# failing.yaml
sources:
  parentSource:
    kind: shell
    spec:
      command: echo olblak
conditions:
  checkUsernameFile:
    kind: file
    spec:
      file: toto;yaml
  checkUsernameFileEmpty:
    kind: file
    spec:
      file:
  checkUsernameYaml:
    kind: yaml
    spec:
      file: toto;yaml
      key: github.username

go build -o dist/updatecli && ./dist/updatecli --config ./failing.yaml

Additional Information

Tradeoff

Potential improvement

[dduportal]

@olblak I've added this (patch) PR to the 0.16.1. Sounds good to you?