upgrade: Show technical debt #899

Feature Request

Show technical debt numbers in cargo upgrade similar to like badges do to encourage increasing maintainability, minimizing vulnerabilities, improving code and using new features.
The simplest number would be to sum up days between the installed version and the last stable release for all found upgrades (12 days between the old and new version of the first upgrade, 34 days between the old and new version of the second upgrade, ...).
If you count compatible and incompatible updates separately you can show the reduced technical debt after a successful upgrade and the remaining technical debt for incompatible upgrades.

Example:

$ cargo upgrade --verbose
    Checking rewrk's dependencies
name  old req compatible latest new req note         debt
====  ======= ========== ====== ======= ====         ====
clap  2       2.34.0     4.5.9  2       incompatible 12 days
http  0.2     0.2.12     1.1.0  0.2     incompatible 34 days
hyper 0.14    0.14.30    1.4.1  0.14    incompatible 56 days
    Technical debt: 102 days
    Checking rewrk-core's dependencies
name  old req compatible latest new req note        
====  ======= ========== ====== ======= ====        
http  0.2     0.2.12     1.1.0  0.2     incompatible 78 days
flume 0.10.14 0.10.14    0.11.0 0.10.14 incompatible 90 days
hyper 0.14    0.14.30    1.4.1  0.14    incompatible 12 days
axum  0.6.20  0.6.20     0.7.5  0.6.20  incompatible 34 days
    Technical debt: 214 days

Please note that crates.io already shows the age of a crate as the very first information below Metadata:

Other package managers like npm and bundler already offer an outdated command, this could be used internally by cargo upgrade and offered as a public command as well.