add a filter to only show test results

[bcressey]

What I'd like: For reporting the results of a testsys run in a PR, it would be useful to limit the output to just the tests.

❯ cargo make testsys status -- --arch aarch64 --tests-only
NAME                            TYPE       STATE       PASSED   SKIPPED   FAILED
aarch64-aws-ecs-1-test          Test       passed      1        0         0
aarch64-aws-k8s-120-test        Test       error       0        0         1
aarch64-aws-k8s-121-test        Test       passed      1        5772      0
aarch64-aws-k8s-122-test        Test       passed      1        6441      0

Bonus feature requests related to sharing the output:

• [ ] right justify numbers within their columns, so digits are in a consistent place
• [ ] add a date or timestamp showing when the most recent state transition happened

Any alternatives you've considered: None.