Contour HTTPProxy support

[josephglanville]

This PR implements support of the Contour HTTPProxy CRD in external-dns using the new LoadBalancer field in Status to propagate endpoints to external-dns.

This requires Contour v1.5.0

Fixes #1366

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[josephglanville]

/cc @stevesloka if you get a chance could you have a look at this? For the most part I tried to re-use what I could from the IngressRoute based source including the same tests. The main difference being instead of specifying which LB service to pull endpoints from we use the LB status on the HTTPProxy objects.

[josephglanville]

/assign @linki

[stevesloka]

Hey @josephglanville, I'll poke around with this next week and have a run in my cluster.

[josephglanville]

Awesome. I will try extend the existing Contour docs during the week too with the additional/alternate RBAC rules.

[josephglanville]

@stevesloka I pushed an update that adds the RBAC rules to the docs and HTTPProxy example.

[josephglanville]

Now that #1627 is merged this is ready for review.

[nikhita]

@linki PTAL :)

[stevesloka]

/lgtm Nice work @josephglanville!! 🎉

Additionally, we should make a plan to remove the IngressRoute support as it's fully deprecated now in Contour, but can wait for the next release to do that work.

[voor]

Really excited for this PR, will help simplify annotations on the Contour Load Balancer Service!

[seanmalloy]

/kind feature

[tariq1890]

@josephglanville Sorry I couldn't get back to this review sooner. Provided comments around error handling as it's better to use one package (going with github.com/pkg/errors since it's already imported).

Can we also have a barebones doc? It doesn't have to be all fleshed out. What I am requesting for is some manifests to help get the user started. A lot of external-dns users face issues from forgetting to specify the right RBAC, for e.g:- We would need to specify get, list as well as watch perms for contour httpproxies since we are using shared informers.

[josephglanville]

I did have docs but I think they got lost in a rebase rejiggering or moving between my machines. I will add those and attend to your review comments shortly. Thanks @tariq1890.

[tariq1890]

/lgtm

Cc @njuettner @Raffo for final approval

[seanmalloy]

/assign @Raffo @njuettner
/unassign @linki

[Raffo]

/approve

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