This allows us to ignore e.g. the last-applied-configuration
annotation by specifying
`metadata.annotations[kubectl.kubernetes.io/last-applied-configuration]`

Needed to cope with multiple levels of bracketed keys

e.g. spec.template.spec[securityContext][runAsUser]

and implementing that lead to a much simpler version
that finds the first key and the rest, and deals with
just those two.

Added more tests to cover some of the new supported
cases.

Ensure test correctly captures that hidden fields should be hidden
in diffs too