fix: return DispatchError in dry-run endpoint

[Imod7]

Description

Closes #1532

Testing

Connected to Westend Asset Hub, when requesting:

curl -X 'POST' \
  'http://127.0.0.1:8080/transaction/dry-run' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "senderAddress": "5F9aniqTwLsRn5ybqSeB2srKfaRXCLeNDSPPHQxPeuGw5Y8a",
  "tx": "0x0a0000fe06fc3db07fb1a4ce89a76eaed1e54519b5940d2652b8d6794ad4ddfcdcb16c0f00d0eca2b99401"
  }'

Before the change we would get the response :

{"at":{"hash":"","height":"0"},"result":{"resultType":"DispatchError","result":{"postInfo":{"actualWeight":null,"paysFee":"Yes"},"error":{"token":"FundsUnavailable"}}}}
{"code":400,"error":"Unable to dry-run transaction","transaction":"0x0a0000fe06fc3db07fb1a4ce89a76eaed1e54519b5940d2652b8d6794ad4ddfcdcb16c0f00d0eca2b99401","cause":"Cannot extract Ok value from Err result, check isOk first","stack":"Error: Cannot extract Ok value from Err result, check isOk first\n    at get asOk [as asOk] (/Users/dominique/Documents/Parity/side-aaFresko/node_modules/@polkadot/types-codec/cjs/base/Result.js:37:19)\n    at TransactionDryRunService.dryRuntExtrinsic (/Users/dominique/Documents/Parity/side-aaFresko/build/src/services/transaction/TransactionDryRunService.js:45:75)\n    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n    at async TransactionDryRunController.dryRunTransaction (/Users/dominique/Documents/Parity/side-aaFresko/build/src/controllers/transaction/TransactionDryRunController.js:62:60)\n    at async /Users/dominique/Documents/Parity/side-aaFresko/build/src/controllers/AbstractController.js:222:9","at":{}}zsh: command not found: at:hash:,result:resultType:DispatchError

After the change we get :

{"at":{"hash":"","height":"0"},"result":{"resultType":"DispatchError","result":{"postInfo":{"actualWeight":null,"paysFee":"Yes"},"error":{"token":"FundsUnavailable"}}}}

[filvecchiato]

Looking good! LGTM