Implement dynamic block installer for our blocks

[finnlewis]

Thanks @tonypaulbarker
Do we want to as a follow up look at the dynamic block installer @rupertj made for installing LGD blocks?

Originally posted by @andybroomfield in #197 (review)

See https://github.com/localgovdrupal/localgov_core/blob/2.x/src/Service/DefaultBlockInstaller.php