Added a dynamic background to the onboarding page

Description

Used linear gradient and keyframes to create moving and changing gradient animation using tinder color-palette to keep the background minimal yet catchy

Related Issue

Fixes #8

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Motivation and Context

For an eye catching background

How Has This Been Tested?

Screenshots (if appropriate):

Checklist:

• I have registered myself at Contrihub website.
• My code follows the code style of this project.
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• Any dependent changes have been merged and published in downstream modules
• I have added tests to cover my changes.
• All new and existing tests passed.

Test Configuration:

• Firmware version:
• Hardware:
• Toolchain:
• SDK: