Update contributing guide to remove Jenkins and add Github Actions (#…

…30595)

* Fix some minor format issues
* Review grammar and links
* Remove mentions to Jenkins in the contributing guide
* Avoid running jobs in forked projects

.github/workflows/binary-compatibility-checks.yml

@@ -12,6 +12,7 @@ jobs:
   check-binary-compatibility:
     name: Check / Binary Compatibility
     runs-on: ubuntu-20.04
+    if: github.repository == 'akka/akka'
     strategy:
       matrix:
         # The versions of scala specified here are only used as `-Dakka.build.scalaVersion=...`

.github/workflows/nightly-builds.yml

@@ -63,6 +63,7 @@ jobs:
   akka-classic-remoting-tests:
     name: Akka Classic Remoting Tests
     runs-on: ubuntu-20.04
+    if: github.repository == 'akka/akka'
     strategy:
       matrix:
         command:
@@ -177,6 +178,7 @@ jobs:
   akka-artery-cluster-tests:
     name: Artery Aeron UDP Cluster
     runs-on: ubuntu-20.04
+    if: github.repository == 'akka/akka'
     strategy:
       matrix:
         command:

.github/workflows/publish-docs.yml

@@ -14,6 +14,7 @@ jobs:
   documentation:
     name: Documentation
     runs-on: ubuntu-20.04
+    if: github.repository == 'akka/akka'
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/publish.yml

@@ -13,6 +13,7 @@ jobs:
   sbt:
     name: sbt publish
     runs-on: ubuntu-20.04
+    if: github.repository == 'akka/akka'
     steps:
       - name: Checkout
         uses: actions/checkout@v2

.github/workflows/scala3-build.yml

@@ -17,6 +17,7 @@ jobs:
   test:
     name: Test
     runs-on: ubuntu-20.04
+    if: github.repository == 'akka/akka'
     strategy:
       matrix:
         command: