Add CPT phage training material to Galaxy training (2nd try)

[jasonjgill]

Adds topics/phage-galaxy/ and one introduction tutorial.md with associated image files. I wasn't sure what other files (e.g., various .yaml files, the /docker/ directory) are strictly needed for function and which are just there as placeholders. I can add/edit these in as needed. The tutorials we have made are all just in .md format, we have not used the slide or other formats.

As requested in discussion with @shiltemann these changes were added to a clean fork of the training-material repo. The contributors.md will need to be updated separately.

[shiltemann]

@jasonjgill thanks a lot! No worries, I can take care of all the technical/infra stuff such as the yaml/docker files you mention.

I will also update the tutorial md files to GTN format and get back to you when I am done, then you can add some of the metadata such as learning objectives, and key points etc.