CDN: avoid cache tags collision (#8969)
We are using `-` as separator
between the project and version slug.
Is easy to generate a collision to generate the same
tag for two or more projects.
For example:
- Project: my-project
Version: latest
Tag: my-project-latest
- Project: my
Version: project-latest
Tag: my-project-latest
A collision can happen on .org if the final tag has 3 or more `-`,
and on .com if the final tag has 4 or more `-` (since we concatenate the
org slug to each project).
This isn't a security issue,
since the cache tag is used only to purge
the cache, not as a key to cache the content.
I've solved this issue by using a character that isn't
allowed on slugs as separator (`:`).
