feat: Add watermark option

[ls-gurvan]

Add Watermark Option Support

This PR adds support for the watermark feature in imgproxy configuration.

Changes

• Added watermark configuration node in Configuration.php
• Added Watermark processing option class

Configuration Options

The watermark option accepts the following parameters:

• opacity: Watermark opacity modifier (float between 0 and 1)
• position: Watermark position - ce (center, default), no, so, ea, we, noea, nowe, soea, sowe, re (repeat)
• x_offset, y_offset: Offset values (integers, default: 0)
• scale: Size relative to the resulting image (float, default: 0 = no resize)

Usage Example

imgproxy:
    options:
        watermark:
            opacity: 0.5
            position: 'soea'
            x_offset: 10
            y_offset: 10
            scale: 0.2

[loicsapone]

Thank you @ls-gurvan!
Sorry for the delay