Create Internal release issue template

Context

Remediating GiLab SaaS single-tenant instances, like GitLab Dedicated, within remediation SLAs requires introducing a new GitLab release strategy: Internal Releases. This release will generate a private package and be delivered to GitLab SaaS single-tenant instances.

Proposal: Create an issue template for the internal release pipeline

Similar to the monthly and patch releases, a template should be created to state all the steps required to perform an internal release.