Change c10d APIs in ProcessGroup to accept const std::vector<at::Tensor>& instead of std::vector<at::Tensor>&.
This is a follow up on #79669.
cc @pietern @mrshenli @pritamdamania87 @zhaojuanmao @satgera @rohan-varma @gqchen @aazzolini @osalpekar @jiayisuse @SciPioneer @H-Huang @kwen2501