Pass knapsack in to tuf autoupdater to simplify configuration

[RebeccaMahany]

Relates to #954.

This is an incremental improvement of TUF work -- passes the knapsack in to the TUF autoupdater. The next piece of work requires some refactoring/configuration changes, and using the knapsack is more flexible.

Subsequent PRs will tackle the following (order is not set in stone):

1. New implementation of findNew (in progress: Draft: TUF find new, v2 #1165)
2. Trigger a reload/restart after a successful update; launcher init performs version selection using the new update library (potentially falling back to findNew); launcher performs library tidying after version selection
3. Other improvements/refactors (ship a more up-to-date TUF repo)
4. An "update now" functionality tied to control server
5. Eventually removing the old notary autoupdater

Previous work:

1. Run new TUF autoupdater side-by-side with notary autoupdater #1081
2. Expose data and metrics about new TUF autoupdater #1103
3. Point to production TUF infra #1108
4. Perform retry on TUF update #1110
5. Add library manager to handle TUF downloads #1111
6. Small autoupdate improvements #1119