feat: add option to provide a redis transport protocol

[so-jd]

My redis server is set to only accept secure redis requests (i.e rediss:// vs redis://), and there was not easy way to set it, Ic created a new variable REDIS_TRANSPORT that defines which transport to use with a default of redis so it will remain backwards compatible and will not introduce breaking changes.

[DawoudSheraz]

You can use openedx-common-settings patch to override settings. I don't think the new config is needed since Tutor provides a way to override the behavior for one's particular requirements.