Adds a nameid tool to the boulder tools directory for SRE use. The
existing local and github CI framework correctly catches build failures
of this directory.
Examples of usage:
```
$ go run ./tools/nameid/nameid.go test/certs/webpki/int-ecdsa-c.cert.pem test/certs/webpki/int-rsa-a.cert.pem
test/certs/webpki/int-ecdsa-c.cert.pem: 56560759852043581
test/certs/webpki/int-rsa-a.cert.pem: 29947985078257530
$ go run ./tools/nameid/nameid.go -s test/certs/webpki/int-ecdsa-c.cert.pem test/certs/webpki/int-rsa-a.cert.pem
56560759852043581
29947985078257530
```
Fixes https://github.com/letsencrypt/boulder/issues/7469
Phil Porada