doc: configuration documentation

[nitrosx]

Description

This PR introduce the first version of a comprehensive list of all the configuration options available. The first options that will be described are the ones related to the header restyle PR

Motivation

While I was getting the header restyle PR, I realized that the FE configuration contains many options and there is no description for them.

Changes:

Please provide a list of the changes implemented by this PR

• adding docs/configuration.md

Tests included

• [ ] Included for each change/fix?
• [ ] Passing? (Merge will not be approved unless this is checked)

Documentation

• [ ] swagger documentation updated [required]
• [ ] official documentation updated [nice-to-have]

official documentation info

If you have updated the official documentation, please provide PR # and URL of the pages where the updates are included

Backend version

• [ ] Does it require a specific version of the backend
• which version of the backend is required:

Summary by Sourcery

Introduce comprehensive frontend configuration documentation and extend header component to leverage configuration options for menu items, branding, and default landing pages, along with related UI refinements and test updates.

New Features:

• Add comprehensive configuration documentation file describing all frontend options

Bug Fixes:

• Update default user thumbnail selector to use colored icon

Enhancements:

• Make header main menu, logo, title, and default landing page driven by config and auth state in AppHeaderComponent
• Refactor AppHeaderComponent to subscribe to login state and apply MainMenuConfiguration and defaultMainPage settings
• Restyle header, breadcrumb, full-text-search-bar, and dataset filter components to adjust button order, colors, margins, and typography

Documentation:

• Add docs/configuration/configuration.md with detailed descriptions for all config options

Tests:

• Update tests to include new config properties in app-config service spec
• Adjust component tests to expect renamed clear button labels