Refactor kubermatic-deploy.sh for argument handling

[steled]

What this PR does / why we need it:

This PR enhances the Helm deployment script to support multiple values.yaml files as separate arguments instead of a single file.
Previously, the script only allowed one values file. With this change, users can pass any number of values files, which Helm will apply in order (later files override earlier ones).
This improves flexibility for complex deployments where configuration is split across multiple files (e.g., base, overrides, secrets).

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

• Argument parsing was refactored:
  • DEPLOY_TYPE remains the first argument.
  • CHART_FOLDER and DEPLOY_STACK are now the last two arguments.
  • All arguments in between are treated as values files.
• Validation ensures at least one values file exists and all provided files are real paths.
• Helm command now expands to multiple --values flags using an array for safe quoting.
• IAP configuration check was updated to scan all provided values files for oidc_issuer_url.

Does this PR introduce a user-facing change?:

Helm deployment script now supports passing multiple values.yaml files as separate arguments:
Old usage:
  ./kubermatic-deploy.sh master values.yaml charts/ logging

New usage:
  ./kubermatic-deploy.sh master base.yaml override.yaml secrets.yaml charts/ logging

Order matters: later files override earlier ones.

[kubermatic-bot]

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[kubermatic-bot]

Hi @steled. Thanks for your PR.

I'm waiting for a kubermatic member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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