clustermesh: Release old connection asynchronously
clustermesh: Release old connection asynchronously

When releasing the etcd connection, sessions are attempted to be
revoked. In the event of an unhealthy etcd connection, the operation
will fail and time out. This operation will take a long time though.
Instead of blocking, release the resources in the background.

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

michi-covalent/cilium,tgraf/cilium,tgraf/cilium,cilium-team/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,cilium/cilium,cilium-team/cilium,cilium/cilium