Allocate GitLab group for Eclipse S-CORE

In the Eclipse S-CORE project, we currently do the project planning using GitHub issues. This has several drawbacks, therefore we were wondering whether there is another tool within Eclipse we could use. Especially we'd request the following features:

• Hierarchical organization of tickets
• Linkage of tickets (e.g. blocked by, implemented by, ...)
• Milestone planning
• Assignment of responsibilie persons
• Adding of new fields to tickets
• Definition of workflows per tickets (e.g. definition how the status of a ticket can be change)

Is there any other open source or free tooling available?