As a preparation for the subsequent commits, let's hard-code the node
key creator and observer implementations, rather than propagating them
through hive, given that they are just tiny wrappers. This simplifies
further extensions, and ensures that we use the same approach in tests
as well, allowing to early catch possible issues.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

Extend the validation performed upon retrieval of node entries from
a remote cluster, to ensure improved consistency and prevent the
propagation of corrupted data. In particular, let's ensure that the
cluster and name fields are always set, that the cluster name matches
that of the cluster we are connected to, and that the name corresponds
to the kvstore key. Additionally, let's provide the possibility of
validating the clusterID correspondence as well.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

Extract and generalize the clustermesh service observer logic,
to additionally reduce code duplication and ensure that the two
usages are always synchronized. While being there, let's also
slightly improve the log messages, and drop the type check, as
always guaranteed to be correct.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

Let's generate the kvstore key and value data representing a shared
service marshalling the ClusterService structure, rather than by
means of strings concatentation. That makes it easier to understand
and extend in the future.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

Extend the validation performed upon retrieval of shared services from
a remote cluster, to ensure improved consistency and prevent the
propagation of corrupted data. In particular, let's ensure that the
cluster, namespace and name fields are always set, that the cluster
name matches that of the cluster we are connected to, and that the
namespaced name corresponds to the kvstore key. Additionally, let's
provide the possibility of validating the clusterID correspondence
as well.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

Now that we enforce the correspondence of the advertised clusterID with
the one present as part of node and service objects, let's add an extra
test to ensure that node and service entries associated with the old
clusterID are eventually drained upon reconnection.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>