fix(connector-polkadot): use dynamic import calls for ESM dependencies

1. The polkadot libraries are all ESM-only so we have to import them
in a specific way in order to avoid runtime crashes.
2. This was not done in the original implementation of the polkadot
connector and because of that all the tests were failing.
3. Refactoring the code so that all polkadot related dependencies are
imported dynamically fixes the issue.
4. Also fixed the issue where the getRawTransaction HTTP REST handler
was not `await` ing for the result of the connector's method which broke
the run-transaction test case (now also fixed)

Fixes #3077

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

packages/cactus-plugin-ledger-connector-polkadot/package.json

@@ -77,7 +77,7 @@
     "express-openapi-validator": "4.13.1",
     "form-data": "4.0.0",
     "fs-extra": "11.2.0",
-    "http-errors": "2.0.0",
+    "http-errors-enhanced-cjs": "2.0.1",
     "http-status-codes": "2.1.4",
     "joi": "17.13.3",
     "multer": "1.4.2",
@@ -94,7 +94,6 @@
     "@hyperledger/cactus-plugin-keychain-memory": "2.0.0-rc.2",
     "@hyperledger/cactus-test-tooling": "2.0.0-rc.2",
     "@types/express": "4.17.21",
-    "@types/http-errors": "2.0.4",
     "@types/joi": "17.2.3",
     "@types/multer": "1.4.7",
     "@types/ssh2": "0.5.44",