Add initial set of Playwright integration tests, for testing embeds (#254)

* add first pass on playwright integration tests!
- test embed loading via localhost:9990/embed.html as well as cross-domain with embed on localhost:8020/
while RWP + data on localhost:9990/
- add --ignore-optional to most ci runs
- add playwright ci test
- add playwright and playwright-test to dev dependencies
- add 'test-start-embed' to start test harness for localhost:8020/ embed
- add 'test-start-sandbox' to start test harndess for localhost:8030/ sandbox
- add additional tests for loading with sandbox + requiresubdomainiframe, ensure 'requiresubdomainiframe' works, doesn't allow loading directly

.github/workflows/lint.yaml

@@ -17,7 +17,7 @@ jobs:
           cache: 'yarn'
 
       - name: Yarn Install
-        run: yarn install --frozen-lockfile
+        run: yarn install --frozen-lockfile --ignore-optional
 
       - name: Yarn Lint
         run: yarn run lint