[helmcli] support YAMLValuesApplier helper function

[fuweid]

In #17, helmcli pkg allows to use key=value path string to update helm values.
For example, a.b.c=v path string is to represent the following YAML value.

a:
  b:
    c: v

kperf/helmcli/release.go

Lines 32 to 41 in 636d5a4

	func StringPathValuesApplier(values ...string) ValuesApplier {
	return func(to map[string]interface{}) error {
	for _, v := range values {
	if err := strvals.ParseInto(v, to); err != nil {
	return fmt.Errorf("failed to parse (%s) into values: %w", v, err)
	}
	}
	return nil
	}
	}

However, StringPathValuesApplier doesn't support array value type.
For instance, for the following YAML value, we can't use key=value format to represent it.

a:
- 1
- 2
- 3

So, we need to introduce new helper function: YAMLValuesApplier.

Since the helm values' type is map[string]interface{}, we need to unmarshal YAML into map[string]interface{} as well and then merge two values.

REF: https://github.com/kubernetes-sigs/yaml