feat: Allow HTTP proxy authentication inputs

[louis-jan]

Specs

Problem Statement

Cortex.cpp now supports proxy configurations with endpoints that enable clients to configure proxy endpoints and authentication.

The PR #4046 aims to restore the HTTP proxy feature, which routes legacy configurations to cortex.cpp. However, it would be beneficial to include more settings that allow users to input authentication credentials, such as username and password, which are essential for most proxy services.

Feature Idea

See attached screenshot:

See cortex.cpp configurations endpoint: https://cortex.so/api-reference#tag/configurations/patch/v1/configs

Acceptance criteria

GIVEN:

1. The cortex.cpp file already supports proxy authentication configurations.
2. Jan has already configured the configurations to be routed to the endpoint.

WHEN:

1. Users go to the app settings page
2. Users input the proxy authentication settings such as username as password

THEN:

1. App should include those settings in the configs request
2. App should allow users to download models via the proxy

Design

Figma link: https://www.figma.com/design/DYfpMhf8qiSReKvYooBgDV/Jan-App-(3rd-version)?node-id=9134-70125&m=dev

User can click on HTTPS Proxy settings from Advanced Settings:

It opens a sub-page for its detailed settings:

[Note] Remove Ignore SSL Certificate here: