Add 'metaplay update sdk' command to help with updating to newer SDK versions.

[petrikero]

Add new command metaplay update sdk that does an update wizard to make it easier to update to a newer Metaplay SDK version.

It does the following:

• Detect version & resolve possible versions to update to (only allow one major version to be done at a time).
• Detect any changes made to the SDK and warn about losing them. In the future, the SDK could try to preserve this using git's change tracking (or similar).
• Update the contents of MetaplaySDK/.
• Link to release notes & instruct to follow migration guide for major releases.