ods-deploy-helm support age for secret management

[gerardcl]

From conversations here: #282

We would like to have a better solution to handle sencrets within helm usage in the ods-pipeline, basically required within ods-deploy-helm and documentation for the initial/updating project and component secrets.

We have seen that age is being recommended to be used by sops and helm-secrets is adding support to it.

The proposal is then to add support for age (make it default) and replace the current default pgp approach.

FYI @renedupont @michaelsauter @kuebler

[gerardcl]

@michaelsauter this does not look like a breaking change, right? do we add it to master right away? or?

[michaelsauter]

@gerardcl Depends how you do it. If we replace PGP, then this is a breaking change. That said, we are pre-1.0, which means any breaking change can be introduced in a minor version. Whatever is in master is going to be released as 0.2.0, so you can introduce the change in master. Personally I am OK with going all-in with age - otherwise we need to test+support two ways of doing the same thing. Until we encounter a use case that needs PGP I would try to live without it.