Add more information to ironic-image release notes about changes in underlying Ironic changes

[tuminoid]

Add more information to ironic-image release notes about changes in underlying Ironic changes. For example, diff between v26.0.0 and v26.0.1 show no changes, as we did no changes in the repository, but since we do not PIN the underlying Ironic branch to a commit, but follow a bugfix branch, it contained changes and the vulnerability fix.

This does not mean we should republish Ironic release notes, but at least link to the commit diff from previous tag in Ironic branch.

[Rozzii]

/triage accepted
I don't think there is much to discuss about this the more info we can give the better.