Add 2.0 release logic (#9467)

This PR:

* Deletes the 2.0 pre-release pipeline
* Causes 1.x releases to be released to Docker Hub without updating the latest tag, PyPI, and the candidate and stable channels of the snap store
* Causes 2.x releases to be released to Docker Hub, PyPI, the beta channel of the snap store, and our Windows installer
We could potentially look into how to continue to do 1.x Windows installer releases through GitHub releases and tech ops tooling, but I personally don't think it's worth it right now.

This PR DOES NOT do anything about progressive snap releases. I think we can revisit this when/if we decide (how) to do them.

.azure-pipelines/2.0-prerelease.yml

@@ -1,18 +0,0 @@
-# Pipeline for testing, building, and deploying Certbot 2.0 pre-releases.
-trigger: none
-pr: none
-
-variables:
-  # We don't publish our Docker images in this pipeline, but when building them
-  # for testing, let's use the nightly tag.
-  dockerTag: nightly
-  snapBuildTimeout: 5400
-
-stages:
-  - template: templates/stages/test-and-package-stage.yml
-  - stage: DeploySnaps
-    jobs:
-      - template: templates/jobs/snap-deploy-job.yml
-        parameters:
-          snapReleaseChannel: beta
-  - template: templates/stages/notify-failure-stage.yml

.azure-pipelines/release.yml

@@ -15,5 +15,11 @@ stages:
   - template: templates/stages/changelog-stage.yml
   - template: templates/stages/deploy-stage.yml
     parameters:
-      snapReleaseChannel: candidate
+      ${{ if startsWith(variables['Build.SourceBranchName'], 'v2') }}:
+        snapReleaseChannel: beta
+      ${{ elseif startsWith(variables['Build.SourceBranchName'], 'v1') }}:
+        snapReleaseChannel: candidate
+      ${{ else }}:
+        # This should never happen
+        snapReleaseChannel: somethingInvalid
   - template: templates/stages/notify-failure-stage.yml