Add support for `OnePlus9`

[OkayRose]

Is your device already requested?

• I have searched the existing issues

Brand

OnePlus

Name

OnePlus 9

Device code

lemonade

Model

LE2115

Device images

No response

Do you own the device and would be willing to test the installer?

• I own the device and am willing to test the installer on it.

Additional context

No response

[tsterbak]

Hi, thanks for your interest in the project!
This device should be not too hard to support.

TWRP: https://twrp.me/oneplus/oneplus9.html
LineageOS: https://wiki.lineageos.org/devices/lemonade/