This change replaces [gorp] with [borp].
The changes consist of a mass renaming of the import and comments / doc
fixups, plus modifications of many call sites to provide a
context.Context everywhere, since gorp newly requires this (this was one
of the motivating factors for the borp fork).
This also refactors `github.com/letsencrypt/boulder/db.WrappedMap` and
`github.com/letsencrypt/boulder/db.Transaction` to not embed their
underlying gorp/borp objects, but to have them as plain fields. This
ensures that we can only call methods on them that are specifically
implemented in `github.com/letsencrypt/boulder/db`, so we don't miss
wrapping any. This required introducing a `NewWrappedMap` method along
with accessors `SQLDb()` and `BorpDB()` to get at the internal fields
during metrics and logging setup.
Fixes#6944
7d66d67054