feat: support image/webp file type (#1415)

* support image/webp file type

Signed-off-by: Elwin <61868295+hzhaoy@users.noreply.github.com>
Signed-off-by: Elwin <hzywong@gmail.com>

* docs: add webp image format in supported_formats.md

Signed-off-by: Elwin <61868295+hzhaoy@users.noreply.github.com>
Signed-off-by: Elwin <hzywong@gmail.com>

* test: add a test case for `image/webp` file

Signed-off-by: Elwin <hzywong@gmail.com>

* style: apply styling

Signed-off-by: Elwin <hzywong@gmail.com>

* test: update test case of converting `image/webp` file with more ocr engines

Signed-off-by: Elwin <hzywong@gmail.com>

* style: apply styling

Signed-off-by: Elwin <hzywong@gmail.com>

* rename test file

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

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Signed-off-by: Elwin <61868295+hzhaoy@users.noreply.github.com>
Signed-off-by: Elwin <hzywong@gmail.com>
Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>
Co-authored-by: Michele Dolfi <dol@zurich.ibm.com>