[Feature] Add EmailIcon to Sistent

[Akshay000000]

Current Behavior

Sistent does not have an EmailIcon component, requiring developers to
depend on @mui/icons-material for this commonly used icon.

Desired Behavior

Create an EmailIcon in Sistent to reduce dependency on
@mui/icons-material and ensure design consistency across Layer5 products.

Implementation

Follow the existing icon pattern in src/icons/ — create
src/icons/Email/EmailIcon.tsx and src/icons/Email/index.tsx,
then export from src/icons/index.ts.

Acceptance Tests

• EmailIcon renders correctly with default width, height, and fill props
• Icon is exported from the main src/icons/index.ts
• Follows the same pattern as other icons in the library

Mockups

https://mui.com/material-ui/material-icons/?query=Email&selected=Email

[Akshay000000]

I'd like to work on this. Can I be assigned?