feat: allow filtering of CertifyVuln query results based on whether they have vulnerabilities

[dejanb]

Description of the PR

This is an attempt to fix #1044 and allow CertifyVuln queries to return only results that include packages with or without vulnerabilities.

For that I changed the semantics of the NoVuln attribute to allow this filtering. This filter could be then used in combination with package filtering.

Some examples of valid queries with this change

1. return all packages with vulnerabilities

query CertifyVuln {
  CertifyVuln(certifyVulnSpec: {
    vulnerability: {noVuln: false}
  }) {
    ...allCertifyVulnTree
  }
}

2. return all openssl packages that have no vulnerabilties

query CertifyNoVuln {
  CertifyVuln(certifyVulnSpec: {
    package: {name: "openssl"},
    vulnerability: {noVuln: true}
  }) {
    ...allCertifyVulnTree
  }
}

All other queries, using no filter, specific vulnerability or package filters should keep working the same

Fixes #1044

PR Checklist

• All commits have a Developer Certificate of Origin (DCO) -- they are generated using -s flag to git commit.
• All new changes are covered by tests
• If GraphQL schema is changed, make generate has been run
• If collectsub protobuf has been changed, make proto has been run
• All CI checks are passing (tests and formatting)
• All dependent PRs have already been merged

[mihaimaruseac]

I like this! Thank you

[pxp928]

LGTM Thanks @dejanb