Remove closed positions; Update issue assignment based on team changes.

[sjwaight]

Two changes:

1. Remove closed positions on README.
2. Update issue assignment based on team changes and added ArgoCD extension auto-assignment.

[Copilot]

Pull request overview

This PR updates repository maintenance files by removing closed job positions and adjusting team member assignments in the issue management policy to reflect current team structure.

• Removes all job listings from README (4 US positions, 1 AUS position) and replaces with "None at present."
• Updates issue auto-assignment policy by removing 2 former team members (danbosscher, pavneeta) across multiple label categories
• Adds new team member (ponatara) to Flux extension handling and creates new ArgoCD extension auto-assignment configuration

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
README.md	Removes closed job postings and replaces with "None at present." to indicate no current openings
.github/policies/manageAssignees.yml	Updates team member assignments across networking, security, and extensions categories; adds ArgoCD extension support with auto-assignment