added pre_backup_cmd to backup items (wip)

[felixandersen]

Opening this PR as I did this change locally and thought it would add value to the role.

I have a changing number of databases I need to backup that need to be dumped to file before each backup. Since the names and numbers are not known at playbook-runtime I cannot use the stdin-feature in this role. My solution is a pre_backup_cmd.

Let me know if this is interesting. I am open to refining the change as needed.

[DO1JLR]

Hi @felixandersen

If I understood it correctly it sounds like a good idea.
But by browsing over the code I am not absoludly sure if I understood it correctly.

Could you give an config example and maybe some minor explaination for the README? 😘

[felixandersen]

I added an example to the README to clarify. That specific pre_backup_cmd however is untested. My deployment runs a separate python-script that does a similar thing.