Start testing on go1.19

[aarongable]

Run the Boulder unit and integration tests with go1.19rc1.

In addition, make a few small changes to allow both sets of tests to run side-by-side. Mark a few tests, including our lints and generate checks, as go1.18-only. Reformat a few doc comments, particularly lists, to abide by go1.19's stricter gofmt.

Causes #6275

[aarongable]

Status update: go1.18 and go1.19 disagree on how to gofmt certain parts of protobuf generated files. Thus, these two versions of Go and our "check that the generated files are correct" test cannot all three live side-by-side in harmony. Therefore I propose (somehow) disabling that check for the go1.19 testing only, and leaving things formatted as go1.18 wants them all the way until we drop go1.18 altogether.

~~I just haven't figured out how to do that yet.~~ nvm I figured out a way