`--sharpness` parameter for DLF sharpness & rate distortion

Description

Issue

This is the first Merge Request from the SVT-AV1-PSY team aiming to integrate our features into mainline SVT-AV1 under the oversight of Hassene Tmar and Faouzi Kossentini. The --sharpness parameter allows users to manually configure deblocking loop filter sharpness, and it also affects rate control. It is used to great effect in SVT-AV1-PSY's Tune 4, which is designed for still image compression; that being said, it still may be useful for perceptual fidelity in video.

By default, sharpness is set to 0 to preserve mainline's default behavior.

Author(s)

Gianni Rosato (@computerbuster)

Clybius

Performance impact

• quality
• memory
• speed
• 8 bit
• 10 bit
• N/A

Test set

• obj-1-fast can be found here
• other
• N/A

Merge method

• Allow the maintainer to squash and merge when PR is ready to create a 1-commit to the master branch. The maintainer will be able to fix typos / combine commit messages to create a more readable 1-commit message or use whatever is stated in the 'Description' section
• I will clean up my commits and the maintainer shall use 'rebase and merge' to the master branch