Add 'x of y tasks completed' into issue#show

Description

You can see how many tasks of an issue are completed on the issues page.
But you can't see that information inside the issue.
When there are a few tasks, it's ok, you can count it manually.
But if there are a few dozen tasks, it's going to be hard to figure out, what's the task completion status now.

For example: #21620 Release 8.12.

79 of 144 tasks completed available only on the all issues page (#index), but you can't see such info inside that issue.

Proposal

Add x of y tasks completed information into issue page.