As part of #571, we want to surface the deprecation information that is
now available upstream in package version lookups, so we can inform our
users about additional cases where packages are deprecated.

This introduces a new table, `depsdev_deprecated` for this purpose, and
populates it with an indication of whether the package is deprecated via
package manager metadata.

We then wire this in so `db generate advisories` can then take the data
and generate a `DEPRECATED` advisory for each package found.

In the future (#593) this will introduce the ability to also surface the
user-facing message, once deps.dev supports it.

We'd ideally have inserted these advisories directly into the
`advisories` table, but by providing them as a utility table (with
messages in the future) it allows for users to query this data directly.

Closes #571.