This commit relaxes k8s api validation pattern for server names in
policy api to allow wildcard specifiers anywhere in SNI pattern.
This allows users to write more compressed network policies and is
inline with the syntax supported in FQDN match pattern.

With this change users can now specify allowed server names with
wildcard as:

- '**.cilium.io': Existing behavior which matches any number of
  subdomain levels in the prefix. "test.cilium.io" and
  "test.app.cilium.io" matches but "cilium.io" does not.

- '*.cilium.io': Existing behavior which matches all subdomains of
  cilium.io on a single level. "test.cilium.io" matches but
  "test.app.cilium.io" and "cilium.io" do not.

- 'sub*.cilium.io': Matches subdomains of cilium.io where the subdomain
  component begins with "sub"(only one level). "sub.cilium.io" and
  "subdomain.cilium.io" matches wile "www.cilium.io", "cilium.io" and
  "test.subdomain.cilium.io" do not.

  Additionally this commit introduces a new helper function used to
  sanitize server names pattern when converting to envoy protobuf. This
  is required because cilium-envoy doesn't support the same semantics
  for match pattern syntax as DNS match pattern in cilium-agent.

Signed-off-by: Deepesh Pathak <deepesh.pathak@isovalent.com>