Improve traffic section in `kn service describe`

[rhuss]

The traffic section kn service describe is confusing as it uses a lot of shortcuts that are not explained anywhere and some revisions appear multiple times (once for when tagged, and one if latest)

[more details to be added ...]

[github-actions[bot]]

This issue is stale because it has been open for 90 days with no activity. It will automatically close after 30 more days of inactivity. Reopen the issue with /reopen. Mark the issue as fresh by adding the comment /remove-lifecycle stale.

[rhuss]

/remove-lifecycle stale

[dsimansk]

/kind good-first-issue

[rhuss]

Well, not sure if this is a "good first issue". Technically it's easy, but it takes some UX experience and background knowledge to get push the description section in the right direction. Maybe we should first discuss here, how we would like the output to look like, and then the implementation should be straight forward.

[vyasgun]

/assign