[all] Support diff mode

[MarkusTeufelberger]

SUMMARY

Most/all modules in here should support returning meaningful diffs on changes.

ISSUE TYPE

• Feature Idea

COMPONENT NAME

ADDITIONAL INFORMATION

It generally feels a bit "empty" if a certificate or similar gets replaced with a simple [changed] notice, having a diff of the actual changes would be really helpful.

See https://blog.networktocode.com/post/generating-diff-with-ansible/ for the general return values expected by Ansible.

Some complications would probably include the fact that there could be private key material leaked and just diffing a DER-encoded file isn't going to help people either... so there should be some way to do the diffs on the parsed + decoded versions of the files we're creating/changing here rather than a straightforward text only diff.

[felixfontein]

Some modules (I think acme_account is one) already have it, and in general it's easy to solve by filling the appropriate output fields.

It's probably easiest if most return fields are put into the diff dict (since these don't contain any private key material).