Add files for building from Rocky8

[amanda11]

Move building of st2chatops for el8 from centos8 to rocky8.

Part of StackStorm/community#88

[amanda11]

Ready for review, but would like to hold out on merge until the st2-packages corresponding PR is ready...

[arm4b]

Considering rockylinux is replacing centos8 for the build, I think there's also a need to remove the inactive centos8 Dockerfiles to avoid confusion in the future

https://github.com/StackStorm/st2chatops/tree/master/packagingenv
https://github.com/StackStorm/st2chatops/tree/master/testingenv

[amanda11]

Considering rockylinux is replacing centos8 for the build, I think there's also a need to remove the inactive centos8 Dockerfiles to avoid confusion in the future

https://github.com/StackStorm/st2chatops/tree/master/packagingenv https://github.com/StackStorm/st2chatops/tree/master/testingenv

Removed them (unfortunate side affect git diff reports them as a move from centos8 to rockylinux8 - but was an add and a delete...)

[arm4b]

Thanks a lot! 👍

[cognifloyd]

Ready for review, but would like to hold out on merge until the st2-packages corresponding PR is ready...

Both of the other PRs have been merged. Merging.

[amanda11]

@cognifloyd Thanks for merge - wasn't online when the changes got approved!