chore: update GitHub configurations and ownership assignments

[Shivam-nagar23]

• Adjust assignees in issue templates (.github/ISSUE_TEMPLATE).
• Refactor CODEOWNERS to streamline ownership.
• Simplify PagerDuty workflow assignees.

Description

Fixes #

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 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/api test cases.

Does this PR introduce a user-facing change?

Summary by Bito

• Updated .github/CODEOWNERS to remove several inactive or reassigned maintainers and streamline ownership.
• Updated issue templates (bug.yaml and pager-duty.yaml) to adjust default assignees.
• Modified the pager-duty-issue-escalate workflow to simplify the escalation assignee list to only include vivek-devtron.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud