Upgrade subsystem overhaul

[btorresgil]

Description

• Support for upgrades to and through 10.2.x
• Add optional behavior to install latest patch of next minor/major release instead of base image.

Motivation and Context

10.2.x is the only minor release that does not have a 0 or 1, so needed to add a special case for it in the upgrade logic.

This new upgrade behavior to use patch releases instead of base images is in-line with modern guidance and best practices. It leverages the latest fixes during upgrades rather than the base image which will have more bugs. Upgrades can take a little longer because 2 images need to be downloaded instead of 1 (the base image and the patch image) but there is still only 1 upgrade for each minor release so this difference is negligible and worth the benefit of using safer patched images as intermediate versions.

NOTE: This new behavior is opt-in. This is not a breaking change.

How Has This Been Tested?

Tested on live firewall and via new test suite.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes if appropriate.
• [x] All new and existing tests passed.

[vrpal]

Hello,

Does this fix suppose to cover upgrade from 10.2.x to 11 ? I'm not having any luck going from 10.2.7 to for example 11.0.2-h2

[shinmog]

@btorresgil

Now sure if this is still needed..? @jamesholland-uk and I did #548 to expand updater logic.