Add flexible configuration of PP-ShiTu detection model

Add shitu android demo2

the ips is unstable in the first 50 iter when training lite modle.

update table_attribute demo imags

fix shitu scenarios doc

fix bugs to adapt to the new framework

add table_attribute docs

update pp-shituv2 doc

fix Constant learning rate bug

update PULC_attr docs

fix bug for warmup_steps setting

In benchmark_train mode, the config name is benchmark.txt. So the keyword of ShiTu should be model_name instead of the config name.