[Web- html,css,javascript] Add eraser to drawing app

[saikatdgp2001]

I have redefined the complete UI and improved some features which are as follows :-

1. Added the "eraser" feature, in which the size of the eraser can be dynamically changed.
2. The slider for the pen size was static in the previous one, and I have created that dynamically so the users can select it from the slider range.
3. Added the background color feature.

Description

Please include a summary of the change and which issue is fixed.

Fixes #(issue_no)

Replace issue_no with the issue number which is fixed in this PR

Type of change

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• [ ] 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)

Checklist:

• [ ] My code follows the style guidelines(Clean Code) of this project
• [ ] I have performed a self-review of my code
• [ ] I have commented on my code, particularly in hard-to-understand areas
• [ ] I have created a helpful and easy-to-understand README.md
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests/screenshots(if any) that prove my fix is effective or that my feature works