update backtest_sites.py

[AUdaltsova]

Pull Request

Description

Decoupled pv padding from data so it uses config instead as had problems running without it and wrong padding (t0 index is not actually the true index when there is not enough data as it's calculated once with respect to proper batch shape and not for each sample)

How Has This Been Tested?

Reran small backtest to check the results ar the same

• [X] Yes

Checklist:

• [X] My code follows OCF's coding style guidelines
• [X] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [X] I have checked my code and corrected any misspellings