Clarify version roll back limitations

[dotproto]

https://extensionworkshop.allizom.org/documentation/publish/version-rollback/

While discussing version roll back with an AMO engineer, they noted that "the restriction for listed channel is that the only version available is the version-before-current." This limitation does not apply to unlisted versions because they do not have a current version.

To make this more concrete, say I currently have version 1.0 approved on AMO and version 2.0 is pending review. After 2.0 is approved, I want to roll back to 1.0 and release that as 2.1. At this point I have two versions: 1.0, 2.0. Since penultimate version is 1.0, I'm able to release that as 2.1.

A week later, I want to roll back to version 2.0 and release it as 2.2. At this point I have three versions: 1.0, 2.0, 2.1. Since the penultimate version is 2.0, I'm able to release that as 2.2.

[abyrne-moz]

The documentation linked explains this with the following statement.

For versions distributed on addons.mozilla.org, the approved version before the current version is available to roll back to.

@dotproto - do you have any suggestions on how we could make this clearer?

[rebloor]

Look through our documentation I'm wondering if we've introduced the term "approved" without really being clear about what it means. (The first time Extension Workshop has mentioned approved extensions is on this page about rollback.) Approved means an extension had passed the human review process, correct?

The other way to phrase this is

For versions distributed on addons.mozilla.org, the most recently approved version is available to roll back to.

or

For versions distributed on addons.mozilla.org, the latest approved version is available to roll back to.

Other than that, we could add the example. But I'm not sure any of these statements are sufficiently ambiguous to need that.

@dotproto I've been removed by assignment, I use assignment as an indication that I'm actively working on an issue.