Fix Kubernetes version string handling by stripping metadata

[Nimbus318]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR fixes an issue where Kubernetes version strings with additional metadata (e.g., +k3s1) caused problems in dynamically generated image tags. The new strippedKubeVersion function removes the part after the + in the Kubernetes version string, ensuring consistent and predictable image tagging.

Which issue(s) this PR fixes:
Fixes #621

Special notes for your reviewer:
@archlitchi
@wawa0210

Does this PR introduce a user-facing change?:
Yes, this PR restores compatibility for specifying certain parameters during helm install/upgrade.

After version 2.4.1, users were unable to specify parameters like scheduler.kubeScheduler.tag (scheduler image version), devicePlugin.deviceSplitCount, devicePlugin.deviceMemoryScaling, and devicePlugin.deviceCoreScaling directly during Helm operations.

With this PR merged:

• Users can now specify the scheduler image version using scheduler.kubeScheduler.tag during helm install or helm upgrade. If the parameter is not provided, the image version will continue to be auto-generated based on the Kubernetes version.
• Parameters like deviceSplitCount, deviceMemoryScaling, and deviceCoreScaling are also restored for direct specification during Helm operations.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Flag	Coverage Δ
unittests	26.80% <ø> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 1 file with indirect coverage changes

[wawa0210]

Very good bug fix, have we done some testing? For example, can it work properly in the K3s environment?

also,you should rebase your commits into one commit

[Nimbus318]

I have rebased the commits into one as requested.

Regarding testing, I have not tested this in a real K3s environment. However, I conducted mock testing for this function locally by injecting a mock Kubernetes version value in _helpers.tpl for validation. Below are the steps I followed:

Mock the Kubernetes version by temporarily injecting a value for testing:

{{/*
    Mock Kubernetes version for testing
*/}}
{{- define "mockedCapabilitiesKubeVersion" -}}
v1.31.1+k3s1
{{- end }}

Modify the existing logic to replace Capabilities.KubeVersion.Version with the mock value:

{{- define "strippedKubeVersion" -}}
{{- $parts := split "+" (include "mockedCapabilitiesKubeVersion" .) -}}
{{- print $parts._0 -}}
{{- end }}

Validated that the output correctly strips the metadata after +.