* feat(tmpl): added fetchSecretValue template function
This adds a tmpl `fetchSecretValue` and `expandSecretRefs` function by:
- Adding:
- `expandSecretRefs` function in tmpl package that uses vals
package to fetch secrets
- `fetchSecretValue` function in tmpl package like below but for
single string value
- gomock for tests purpose
- Changing:
- move init of vals package to function (so the same instance can be used for template values and rendering the whole template)
* doc(secret): added doc how to use new tmpl methods
Added example usage of `fetchSecretValue` and `expandSecretRefs`
Marcin Kaciuba