WPAD support

[saidelike]

Description

Adds opt-in PAC/WPAD proxy auto-configuration support for Jira and Confluence clients. This is needed for environments where outbound Atlassian traffic must be routed through a proxy selected by a PAC
file rather than a static proxy URL.

WPAD is disabled by default. Existing explicit proxy configuration continues to take precedence, and header-based PAT behavior is preserved when WPAD is not enabled.

Fixes: #

Changes

• Added shared proxy utilities for explicit proxy handling, PAC/WPAD loading, PAC validation, session wrapping, and NO_PROXY bypass preservation.
• Added Jira/Confluence config support for global and service-specific WPAD settings.
• Wired Jira and Confluence clients to apply explicit proxy settings or opt-in PAC/WPAD routing.
• Preserved header-based PAT defaults while allowing WPAD settings to be carried when enabled.
• Added .env.example, docs, and Helm chart values/env support for WPAD configuration.
• Added focused tests for proxy config parsing, PAC/WPAD session behavior, OAuth target URL selection, and server dependency behavior.

Testing

• Unit tests added/updated
• Integration tests passed
• Manual checks performed: uv sync --frozen, focused pytest suite, full pytest suite, and ruff check for new proxy utility`

Checklist

• Code follows project style guidelines (linting passes).
• Tests added/updated for changes.
• All tests pass locally.
• Documentation updated (if needed).