Add additional audit strategies

[perama-v]

Description

At present the strategies are:

• latest
• random
• failed (prev missing)

New strategies suggested:

And then I think in the future we'd also want a Missing strategy that looks up data that has never been audited, but not necessarily the newest. Maybe OldestMissing that works its way forward from the beginning of the chain.

Originally posted by @mrferris in https://github.com/pipermerriam/glados/pull/60#discussion_r1106250734