revisit the ManagedClusterConditionAvailable condition

[haoqing0110]

Describe the enhancement
Today the ManagedCluster condition ManagedClusterConditionAvailable status could be True, False and Unknown.
The status is set to false when kube API server is unavailable, and to unknown when lease stop update.
Some feedback shows that this condition will be flapping, for example, when API server is not stable. Log this issue to revisit the conditions to set ManagedClusterConditionAvailable status.

[haoqing0110]

cc @qiujian16

[haoqing0110]

cc @haowells

[github-actions]

This issue is stale because it has been open for 120 days with no activity. After 14 days of inactivity, it will be closed. Remove the stable label to prevent this issue from being closed.