audit: add Cantina security review for v1.1.1 (#1625)

Note on commits: the security review was done on commit
0f94c8a
(tag v1.0.1-rc.1). This was rebased on top of the security fix from
v1.1.0 to commit
b4a5652
(tag v1.1.1-rc.1).

One can check via
```bash
git diff b4a5652 0f94c8a
```
that the only difference in the two commits is the fix from
v1.1.0..v1.0.0.

Author: jonathanpwang