MNT: Add issue/PR templates

[leofang]

• Ask users to provide their environment info
• Direct users to ask questions in GH Discussions not Issue Tracker (Add issue config #345)
• ...

[leofang]

@kkraus14 has done most of the work. We can improve the templates gradually. Let me use this issue to note that I need users to report their Python environment (pip list/conda list/nvidia-smi/...) to know which CTK/driver versions are in use.