Add 1.5.1 release notes (#2912)

* Add 1.5.1 release notes

Prepare for imminent release.
Also list PRs merged in a new section to provide more detail.
Signed-off-by: Miek Gieben <miek@miek.nl>

* Updates after review
Signed-off-by: Miek Gieben <miek@miek.nl>

notes/coredns-1.5.1.md

++++
+title = "CoreDNS-1.5.1 Release"
+description = "CoreDNS-1.5.1 Release Notes."
+tags = ["Release", "1.5.1", "Notes"]
+release = "1.5.1"
+date = "2019-06-20T13:03:07+00:01"
+author = "coredns"
++++
+
+The CoreDNS team has relased
+[CoreDNS-1.5.1](https://github.com/coredns/coredns/releases/tag/v1.5.1).
+
+Various bugfixes, better documentation and cleanups.
+
+The `-cpu` flag is somewhat redundant (cgroups/systemd/GOMAXPROCS are better ways to deal with
+this) and we want to remove it; if you depend on it in some way please voice that in [this
+PR](https://github.com/coredns/coredns/pull/2793) otherwise we'll remove it in the next release.
+
+# Plugins
+
+* A new plugin [*any*](/plugins/any) that block ANY queries according to [RFC 8482](https://tools.ietf.org/html/rfc8482) was added.
+* Failed reload fixes for: [*ready*](/plugins/ready), [*health*](/plugins/health) and [*prometheus*](/plugins/metrics) - when CoreDNS reloads and the Corefile is invalid these plugins now keep on working.
+* [*tls*](/plugins/tls) now has a `client_auth` option that allows verification of client TLS certificates. Note that the default behavior continues to be to not require validation, however in version 1.6.0 this default will change to `required_and_verify` if the CA is provided.
+* [*kubernetes*](/plugins/kubernetes) can now publish metadata about the request and, if `pods verified` is enabled, about the client Pod. To enable this, you must enable the [*metadata*](/plugins/metadata) plugin.
+  And also return pod IPs for running pods, instead of just the first
+  ([PR](https://github.com/coredns/coredns/pull/2846) and
+  [PR](https://github.com/coredns/coredns/pull/2853)
+
+* The [*cache*](/plugins/cache) now sets the Authoritative bit on replies
+  ([PR](https://github.com/coredns/coredns/pull/2885)). Further more it also caches DNS
+  failures ([PR](https://github.com/coredns/coredns/pull/2720))
+
+## Brought to You By
+
+Alyx,
+Andras Spitzer,
+Andrey Meshkov,
+Anshul Sharma,
+Anurag Goel,
+An Xiao,
+Billie Cleek,
+Chris O'Haver,
+Cricket Liu,
+Francois Tur,
+JINMEI Tatuya,
+John Belamaric,
+Kun Chang,
+Michael Grosser,
+Miek Gieben,
+Sandeep Rajan,
+varyoo,
+Yong Tang.
+
+## Noteworthy Changes
+
+* build: Add CircleCI for Integration testing (https://github.com/coredns/coredns/pull/2889)
+* core: Add server instance to the context in ServerTLS and ServerHTTPS (https://github.com/coredns/coredns/pull/2840)
+* plugin: Add any plugin (https://github.com/coredns/coredns/pull/2801)
+* plugin/cache: cache failures (https://github.com/coredns/coredns/pull/2720)
+* plugin/cache: remove item.Autoritative (https://github.com/coredns/coredns/pull/2885)
+* plugin/chaos: randomize author list (https://github.com/coredns/coredns/pull/2794)
+* plugin/health: add OnRestartFailed (https://github.com/coredns/coredns/pull/2812)
+* plugin/kubernetes: make ignore empty work with ext svc types (https://github.com/coredns/coredns/pull/2823)
+  plugin/kubernetes: never respond with NXDOMAIN for authority label (https://github.com/coredns/coredns/pull/2769)
+* plugin/kubernetes: Publish metadata from kubernetes plugin (https://github.com/coredns/coredns/pull/2829)
+* plugin/kubernetes: skip deleting pods (https://github.com/coredns/coredns/pull/2853)
+* plugin/loop: Update troubleshooting step (https://github.com/coredns/coredns/pull/2804)
+  plugin/metrcs: fix datarace on listeners (https://github.com/coredns/coredns/pull/2835)
+* plugin/metrics: fix failed reload (https://github.com/coredns/coredns/pull/2816)
+* plugin/ready: fix starts and restarts (https://github.com/coredns/coredns/pull/2814)
+* plugin/template: Raise error if regexp and template are not specified together (https://github.com/coredns/coredns/pull/2884)
+* tls: make sure client CA and auth type are set if CA is explicitly specified. (https://github.com/coredns/coredns/pull/2825)