etcd-e2d-test:rename e2e-arm64 file and runs it on every pull request

Recently in etcd-io#16801 we introduced on demand github actions runners for the arm64 platform.
Having on demand runner infrastructure in place means we should now have enough capacity to begin running arm64 tests for every pull request.
Currently we have:
.github/workflows/e2e-arm64-template.yaml - Shared template
.github/workflows/e2e-arm64-nightly.yaml - Runs template against both release-3.5 and main branches nightly.
Moving forward we can just rename .github/workflows/e2e-arm64-template.yaml to .github/workflows/e2e-arm64.yaml and delete the other file. We can then just make the template file a standard workflow that will run on pull request.

Signed-off-by: Ming Li <mli103hawk@gmail.com>

.github/workflows/e2e-arm64-template.yaml → .github/workflows/e2e-arm64.yaml

@@ -1,11 +1,6 @@
 ---
 name: Reusable Arm64 E2E Workflow
-on:
-  workflow_call:
-    inputs:
-      etcdBranch:
-        required: true
-        type: string
+on: [push, pull_request]
 permissions: read-all
 jobs:
   test:
@@ -20,7 +15,7 @@ jobs:
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
-          ref: "${{ inputs.etcdBranch }}"
+          ref: "main"
       - id: goversion
         run: echo "goversion=$(cat .go-version)" >> "$GITHUB_OUTPUT"
       - uses: actions/setup-go@93397bea11091df50f3d7e59dc26a7711a8bcfbe # v4.1.0