New repo request: phosphor-psu-code-mgmt

[Lei YU]

Hi Brad,

Could you please help to create a new repo for PSU firmware management?
It could be named like `phosphor-psu-code-mgmt` which is consistent to existing
phosphor-[bmc|pnor]-code-mgmt, or maybe help to suggest another name?

The design doc is under review and it looks like it's going to be accepted:
https://gerrit.openbmc-project.xyz/c/openbmc/docs/+/22821

Thanks!