fix(): Added missing resources and fix SecurityContext for OpenVPN gateway containers

[Alokzh]

Description

This PR fixes missing resource specifications and overly permissive security contexts in OpenVPN gateway containers within slice gateway pod specifications.

Fixes: #363 , #364 , #365 , #366

Changes Made:

• Added resource limits and requests for OpenVPN server (256Mi memory, 200m CPU)
• Added resource limits and requests for OpenVPN client (128Mi memory, 100m CPU)
• Updated SecurityContext for both containers to use minimum required permissions

How Has This Been Tested?

Tested with KubeSlice minimal-demo setup. Verified that gateway pods now have proper resource specs and security improvements without breaking functionality.

Checklist:

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR requires documentation updates?
• I've updated documentation as required by this PR.
• I have ran go fmt
• I have updated the helm chart as required by this PR.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have tested it for all user roles.
• I have added all the required unit test cases.
• I have verified the E2E test cases with new code changes.
• I have added all the required E2E test cases.

Does this PR introduce a breaking change?

[pnavali]

@gourishkb - please review the PR.