Currently only implemented to kubectl-style deployments.
Helm support to be added in the next commits.

This is a breaking change for the self-sharding configuration.
Configs previously expressed in the self-sharding object are
now moved to self-sharding.shard. In addition, the optional
array self-sharding.conditions may express conditions under
which self-sharding logic is executed.

The conditions array has the same syntax and semantics as
for req-disposition.

XXX: there is some DRY that needs to be refactored away.

- We currently have two internal means of expressing
  conditions under which something happens (translated
  to if-clauses with matching operations and the like in
  VCL): Condition and the legacy MatchTerm, in both the
  k8s VarnishConfig class and the spec type for VCL
  templating. These should be unified to Condition.

- The code for interpreting Conditions for the k8s object
  in pkg/controller is in part repeated for self-sharding
  and req-disposition. These should be encapsulated in a
  common function.

- Template generation for the if-clauses implementing
  conditions is repeated in req-dispostiion and currently
  in two places for self-sharding. This should be a
  common text/template object.

While here, move some of the code about self-sharding and
conditions from varnishconfig.go to ingress.go. Because
it's actually about the VarnishConfig Custom Resource, and
in a continuing effort to reduce the oversized ingress.go
source.