multi: itest jobs with SQL graph backend

In this commit, a new `test_native_sql` build flag is defined. If this
build flag is used along with the `--use-native-sql` config option, then
the SQLStore implementation of the graphdb.V1Store will be initialised.
This is then used to run our itest suite against the new SQLStore graph
implementation.

NOTE that this only works for new nodes currently - the migration from
kv-to-sql is yet to be implemeneted.

.github/workflows/main.yml

@@ -368,10 +368,14 @@ jobs:
             args: backend=bitcoind dbbackend=sqlite
           - name: bitcoind-sqlite-nativesql
             args: backend=bitcoind dbbackend=sqlite nativesql=true
+          - name: bitcoind-sqlite=nativesql-experiment
+            args: backend=bitcoind dbbackend=sqlite nativesql=true tags=test_native_sql
           - name: bitcoind-postgres
             args: backend=bitcoind dbbackend=postgres
           - name: bitcoind-postgres-nativesql
             args: backend=bitcoind dbbackend=postgres nativesql=true
+          - name: bitcoind-postgres-nativesql-experiment
+            args: backend=bitcoind dbbackend=postgres nativesql=true tags=test_native_sql
     steps:
       - name: git checkout
         uses: actions/checkout@v4