Related to #494
This feature is mostly a built-in alternative to the `incubator/raw` chart without external dependency and has
access to helmfile's own template functions and template data.
The expected use-case of this feature is to add arbitrary K8s resources to your deployment.
Unlike the original issue raised in #494 this doesn't enable you to add arbitary resources to a release. That's another story. But this would be a good foundation for that, too.
Enhances Helmfile to print more helpful message on error while calling `exec` template function.
Helmfile has been printing error messages like the below:
```
in ./helmfile.yaml: error during helmfile.yaml.part.0 parsing: template: stringTemplate:5:8: executing "stringTemplate" at <exec "./exectest.sha" (list)>: error calling exec: exit status 1
```
Adding captured stdout and stderr, with some indentation to make it readable, it now produces the following message on missing executable:
```
$ make build && ./helmfile build
go build
in ./helmfile.yaml: error during helmfile.yaml.part.0 parsing: template: stringTemplate:5:8: executing "stringTemplate" at <exec "./exectest.sha" (list)>: error calling exec: fork/exec ./exectest.sha: no such file or directory
COMMAND:
./exectest.sha
ERROR:
fork/exec ./exectest.sha: no such file or directory
```
On non-zero exit status without output:
```
$ make build && ./helmfile build
go build
in ./helmfile.yaml: error during helmfile.yaml.part.0 parsing: template: stringTemplate:5:8: executing "stringTemplate" at <exec "./exectest.sh" (list)>: error calling exec: exit status 1
COMMAND:
./exectest.sh
ERROR:
exit status 1
```
On non-zero exit status with output:
```
$ make build && ./helmfile build
go build
in ./helmfile.yaml: error during helmfile.yaml.part.0 parsing: template: stringTemplate:5:8: executing "stringTemplate" at <exec "./exectest.sh" (list)>: error calling exec: exit status 2
COMMAND:
./exectest.sh
ERROR:
exit status 2
COMBINED OUTPUT:
out1
err1
```
Resolves#1158
Seems like we are affected by https://github.com/golang/go/issues/24963. That is, even though we internally use the template option `missingkey=zero`, in some cases it still prints `<no value>` instead of zero values, which has been confusing the state yaml parsing.
This fixes the issue by naively replacing all the remaining occurrences of `<no value>` in the rendered text, while printing debug logs to ease debugging in the future when there is unexpected side-effects introduced by this native method.
Fixes#553