Make it possible to back up and restore custom rules created from templates

SonarQube currently provides the ability to back up and restore quality profiles, which must contain only the activation details of rules within a profile.

But there is currently no way to back up and restore all the customizations done on the rules themselves:

• Extended description on any kind of rule
• Set of tags on a rule (including custom tags)
• Custom rules created from rule templates

Example of use case: you want to synchronize your production environment with the pre-production environment on which you create some custom rules.

With this ticket, only export/import of custom rules will be implemented. Customizations rules import will be done in separate one.