RAM versions of MySQL

[TomK]

These "in-memory" mysql images have not been ported over to the new convenience images yet.

old:
https://github.com/CircleCI-Public/circleci-dockerfiles/blob/master/mysql/images/5.7.33/ram/Dockerfile

[ryanwohara]

https://github.com/CircleCI-Public/cimg-mysql#ram

[TomK]

On the old images the difference was significant. I've since run some tests against the new image and they seem to be equivalent in run time to the old RAM image. Closing.