fix(core): Handle K8s service account token rotation

[AryanBakliwal]

Purpose of PR?:
Use BearerTokenFile in client config, which is set to the path to a file containing BearerToken. The contents of the file are periodically read and the last successfully read value takes precedence over BearerToken.

Fixes #2262

Does this PR introduce a breaking change?
No

If the changes in this PR are manually verified, list down the scenarios covered:
Using a local k3s cluster and setting token expiration time to 1 hour. See timestamp in logs:

Before
After ~1 hour, the token expires and requests to API server return unauthorized

$ kubectl logs -n kubearmor kubearmor-bpf-containerd-2c350-5z8tf 

2026-03-12 16:46:35.651297	INFO	BUILD-INFO: version: v1.6.8-dirty, branch: HEAD, date: 2026-02-04T09:57:14Z
...
2026-03-12 16:46:35.659895	INFO	Initialized Kubernetes client
...
2026-03-12 17:48:03.890848	INFO	[ProtectProc] deleting container with id to protectProc_map exec map: 708e36794693dde1bc8b2cec90830e08b4ccd26ca76811c3c35cab95157beb27

E0312 17:48:33.107939       1 reflector.go:205] "Failed to watch" err="failed to list *v1.ConfigMap: Unauthorized" logger="UnhandledError" reflector="pkg/mod/k8s.io/client-go@v0.34.1/tools/cache/reflector.go:290" type="*v1.ConfigMap"
E0312 17:49:25.584014       1 reflector.go:205] "Failed to watch" err="failed to list *v1.ConfigMap: Unauthorized"
...

After
KubeArmor pod running for >1.5 hour, working as expected

$ kubectl get pods -n kubearmor                                                                                                                                   

NAME                                    READY   STATUS    RESTARTS   AGE
kubearmor-bpf-containerd-2c350-d4jzf    1/1     Running   0          91m
kubearmor-controller-6cff7cdcb8-gx9d9   1/1     Running   0          91m
kubearmor-operator-574f9967ff-hkx65     1/1     Running   0          93m
kubearmor-relay-6f5445f967-nt89m        1/1     Running   0          92m

$ kubectl logs -f -n kubearmor kubearmor-bpf-containerd-2c350-d4jzf

2026-03-12 18:30:19.219019	INFO	BUILD-INFO: version: v1.6.14-dirty, branch: fix-sa-token-rotation, date: 2026-03-12T17:56:24Z
...
2026-03-12 18:30:19.221908	INFO	Initialized Kubernetes client
...
2026-03-12 20:04:03.864832	INFO	Namespace pentestit visibiliy configured {File:true Process:true Network:true Capabilities:true DNS:false IMA:false}

Additional information for reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• Bug fix. Fixes KubeArmor daemonset losing auth. to K8s API after 24 hours #2262
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• PR Title follows the convention of <type>(<scope>): <subject>
• Commit has unit tests
• Commit has integration tests