Ignore copy file on missing source

[ademariag]

Fixes issue #688

Proposed Changes

Allows the "copy" input type to continue even if the source path is missing.

The main motivation behins this change is to enable a workaround to handle terraform lock files which are now being produced when running terraform init, see hashicorp/terraform#27241

The solution would be to allow adding the following copy settings:

 kapitan:
    compile:
      - input_type: copy
        ignore_missing: true
        input_paths:
          - resources/state/${target_name}/.terraform.lock.hcl
        output_path: terraform/

Without this feature, the compile process would fail for all new environments where the state file has not already been placed in the state folder.

[ramaro]

I guess it's better to raise CompileError to keep kapitan error handling/printing consistent

[ademariag]

@ramaro I used the same error that was already raised in line 39. Shall I also change that?