remove "site" from SiteBatchkey

[peterdudfield]

It would be good to remove the extra work fo site fomr the SitebatchKey

https://github.com/openclimatefix/ocf-data-sampler/blob/main/ocf_data_sampler/numpy_batch/site.py#L9

Other bits of code would also need updating. So site_capacity_kwp = "site_capacity_kwp" would go to
capacity_kwp = "site_capacity_kwp"

[alirashidAR]

Hi @peterdudfield,

I’ve been exploring the organization’s projects and, to gain a better understanding, I’d like to contribute by resolving some smaller issues. Would it be okay if I take this up?