[CLIP] fix logit_scale init
# What does this PR do?

This PR fixes the initialization of `logit_scale` parameter as per the [original CLIP implementation ](https://github.com/openai/CLIP/blob/3b473b0e682c091a9e53623eebc1ca1657385717/clip/model.py#L291).

Also, the initial value of `logit_scale` needs to be carefully tuned for CLIP training, so this PR, adds a `logit_scale_init_value` as a `config` parameter, so users could pass different init values as per their training.


Fixes #13430