Add a workflow for publishing flutter packages

Closes #1259

Add a second copy of the publish workflow with `use-flutter: true`.
Add `ignore-packages` to both workflows to ignore published packages for
the non-relevant SDK.

Author: natebosch

Diff for: .github/workflows/publish.yaml

@@ -1,6 +1,6 @@
 # A CI configuration to auto-publish pub packages.
 
-name: Publish
+name: Publish Dart Packages
 
 on:
   pull_request:
@@ -15,3 +15,4 @@ jobs:
     permissions:
       id-token: write # Required for authentication using OIDC
       pull-requests: write # Required for writing the pull request note
+    ignore-packages: pkgs/cupertino_http/,pkgs/cronet_http/,pkgs/ok_http/

Diff for: .github/workflows/publish_flutter.yaml

@@ -0,0 +1,19 @@
+# A CI configuration to auto-publish pub packages.
+
+name: Publish Flutter Packages
+
+on:
+  pull_request:
+    branches: [ master ]
+  push:
+    tags: [ '[A-z]+-v[0-9]+.[0-9]+.[0-9]+' ]
+
+jobs:
+  publish:
+    if: ${{ github.repository_owner == 'dart-lang' }}
+    uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main
+    permissions:
+      id-token: write # Required for authentication using OIDC
+      pull-requests: write # Required for writing the pull request note
+    use-flutter: true
+    ignore-packages: pkgs/http/,pkgs/http_profile/,pkgs/web_socket/,