Add GVK to post-build error message

[maboehm]

We recently had a syntax error in an env substitution, but all we saw in the cluster was

post build failed for '${NAME}': envsubst error: variable substitution failed: unable to parse variable name

because in the manifest we used templated the resource name:

metadata:
  name: ${NAME}

The error was quite confusing in that case. In general, the resource name itself might not be enough to pin-point an issue, since is is common to have the same name across e.g. a Deployment and a Service.

[stefanprodan]

@maboehm can you please sign-off the commit, instructions here: https://github.com/fluxcd/kustomize-controller/pull/1547/checks?check_run_id=54698541732

[stefanprodan]

LGTM

Thanks @maboehm

[fluxcdbot]

Successfully created backport PR for release/v1.7.x:

• [release/v1.7.x] Add GVK to post-build error message #1555