[Datahub] Updated styling for the navigation-button and language-switcher

[ronitjadhav]

Description

This PR updates the styling for the navigation button (back button) and language switcher, which fixes the issue of text not being visible when the background is white.

• Updated style of navigation button to use the colour from the "header_foreground_color" setting from the config.
• Update style for the language switcher text
• All text in the header should be the same colour and that color should be the header_foreground_color setting from the config

Quality Assurance Checklist

• Commit history is devoid of any merge commits and readable to facilitate reviews
• If new logic ⚙️ is introduced: unit tests were added
• If new user stories 🤏 are introduced: E2E tests were added
• If new UI components 🕹️ are introduced: corresponding stories in Storybook were created
• If breaking changes 🪚 are introduced: add the breaking change label
• If bugs 🐞 are fixed: add the backport <release branch> label
• The documentation website 📚 has received the love it deserves

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This work is sponsored by Organization ABC.

[github-actions]

Affected libs: ui-catalog, feature-catalog, feature-record, feature-router, ui-inputs, feature-dataviz, feature-search, feature-map, feature-editor, ui-elements, ui-search, ui-layout,
Affected apps: datahub, metadata-editor, demo, webcomponents, map-viewer, search, metadata-converter, datafeeder,

• 🚀 Build and deploy storybook and demo on GitHub Pages
• 📦 Build and push affected docker images

[coveralls]

coverage: 82.262% (-1.0%) from 83.263%
when pulling 392a352 on fix-text-not-visible
into 5042be2 on main.