step-ca: Redeploy with DCH CA R3

I never ended up using _Step CA_ for anything, since I was initially
focused on the SSH CA feature and I was unhappy with how it worked
(which led me to write _SSHCA_).  I didn't think about it much until I
was working on deploying Grafana Loki.  For that project, I wanted to
use a certificate signed by a private CA instead of the wildcard
certificate for _pyrocufflink.blue_.  So, I created *DCH CA R3* for that
purpose.  Then, for some reason, I used the exact same procedure to
fetch the certificate from Kubernetes as I had set up for the
_pyrocufflink.blue_ wildcard certificate, as used by Frigate.  This of
course defeated the purpose, since I could have just as easily used
the wildcard certificate in that case.

When I discovered that Grafana Loki expects to be deployed behind a
reverse proxy in order to implement access control, I took the
opportunity to reevaluate the certificate issuance process.  Since a
reverse proxy is required to implement the access control I want (anyone
can push logs but only authenticated users can query them), it made
sense to choose one with native support for requesting certificates via
ACME.  This would eliminate the need for `fetchcert` and the
corresponding Kubernetes API token.  Thus, I ended up deciding to
redeploy _Step CA_ with the new _DCH CA R3_ for this purpose.

argocd/applications/step-ca.yaml

@@ -0,0 +1,13 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: step-ca
+  namespace: argocd
+spec:
+  destination:
+    server: https://kubernetes.default.svc
+  project: default
+  source:
+    path: step-ca
+    repoURL: https://git.pyrocufflink.blue/infra/kubernetes.git
+    targetRevision: master