Fix #1943: allow multiple operators to reconcile label filtered resources

[nicolaferraro]

Fix #1943

Multiple operators can be configured to only reconcile resources marked with label camel.apache.org/operator.id=<the-operator-id>. This helps e.g. with externally coordinated upgrades.

The operator ID can be set on the operator via the KAMEL_OPERATOR_ID env variable.
By default, normally installed operators (i.e. without ID) don't reconcile resources with a camel.apache.org/operator.id label, so this makes it possible for scoped global operators to share a cluster with a standard global operator.

Release Note

It's possible to assign an ID to a Camel K operator in order to reconcile only a specific set of resources

[astefanutti]

Great, with this we have multi-tenancy for descoped/global operator!

I'm wondering if there are any reasons that prevent the filtered to be configured at the cache level, like in https://github.com/apache/camel-k/blob/f62e640b2dd422cf5195671ef248dfbadbc92056/pkg/cmd/operator/operator.go. That would prevent the overhead of caching the resources that do not match, as well as sparing the filtering of the associated reconciliation requests.