Add io-thread daily CI tests. (#8232)

This adds basic coverage to IO threads by running the cluster and few selected Redis test suite tests with the IO threads enabled.

Also provides some necessary additional improvements to the test suite:

* Add --config to sentinel/cluster tests for arbitrary configuration.
* Fix --tags whitelisting which was broken.
* Add a `network` tag to some tests that are more network intensive. This is work in progress and more tests should be properly tagged in the future.

.github/workflows/daily.yml

@@ -99,6 +99,23 @@ jobs:
         ./runtest-cluster --tls
         ./runtest-cluster
 
+  test-ubuntu-io-threads:
+    runs-on: ubuntu-latest
+    if: github.repository == 'redis/redis'
+    timeout-minutes: 14400
+    steps:
+    - uses: actions/checkout@v2
+    - name: make
+      run: |
+        make
+    - name: test
+      run: |
+        sudo apt-get install tcl8.5 tcl-tls
+        ./runtest --config io-threads 4 --config io-threads-do-reads yes --accurate --verbose --tags network
+    - name: cluster tests
+      run: |
+        ./runtest-cluster --config io-threads 4 --config io-threads-do-reads yes
+
   test-valgrind:
     runs-on: ubuntu-latest
     if: github.repository == 'redis/redis'