Support regex with "?!" in HTTPProxy

[jadefr]

I get the following error when creating HTTPProxy with "?!":

  - errors:
    - message: 'route: supplied regex: /lorem/(?!.*\/ipsum)(.*) invalid. error: error
        parsing regexp: invalid or unsupported Perl syntax: `(?!`'
      reason: PathMatchConditionsNotValid
      status: "True"
      type: RouteError

Steps to reproduce:

Deploy yaml:

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: basic
spec:
  virtualhost:
    fqdn: foo-basic.bar.com
  routes:
    - conditions:
      - regex: /lorem/(?!.*\/ipsum)(.*)
      services:
        - name: s1
          port: 80

I believe using package regexp2 would solve the issue.
As an example, the following PR was done in NGINX Virtual Server: nginxinc/kubernetes-ingress#4465

[github-actions]

Hey @jadefr! Thanks for opening your first issue. We appreciate your contribution and welcome you to our community! We are glad to have you here and to have your input on Contour. You can also join us on our mailing list and in our channel in the Kubernetes Slack Workspace

[tsaarni]

Hi @jadefr. the validation Contour does using Go’s regexpshould align with Google’s RE2 engine as used in Envoy. It appears that NGINX uses PCRE, which does support negative lookaheads.