Fix: correct kubectl command execution by removing absolute path

[cuonghm2809]

Issue Description:

The application encountered an error where the kubectl command could not be executed because it was referenced with an absolute path (/kubectl). The error message fork/exec /kubectl: no such file or directory indicates that the command was not found at the specified path. This issue occurs because kubectl should be invoked using its relative or full path based on the environment configuration, rather than assuming a fixed location.

{"level":"info","caller":"drainmanager/kubernetes.go:54","msg":"uncordon node aks-agent-312112314-vmss000000"}
{"level":"error","msg":"fork/exec /kubectl: no such file or directory","command":"kubectl"}

Steps to Reproduce:

Attempt to run the drain function that triggers the kubectl command.
Observe the error message related to /kubectl not being found.
Expected Behavior: The kubectl command should execute successfully, allowing proper drain handling in the Kubernetes environment.

Actual Behavior: The execution fails with the error no such file or directory due to an incorrect path reference for kubectl.

[aslafy-z]

See #18

[mblaschke]

merged and fixed with 25.2.1