Issue with Default Handler in resolver

[kesha-shah]

Describe the bug
With this commit, there is one issue caused which is blocking us to use default exported functions in APIs

To Reproduce

1. Use any version > 4.13.2 - This bug got introduced in version 4.13.4
2. Create one HTTP API function, export it as default function, set it as operationId and set its path in x-eov-operation-handler
3. Try to invoke that API

Actual behavior
It gives error Route.get() requires a callback function but got a [object Object]
Stacktrace :

Route.get() requires a callback function but got a [object Object]\n at Route. [as get] (/Users/keshashah/work/api-framework/node_modules/express/lib/router/route.js:211:15)\n at Function.proto. [as get] (/Users/keshashah/work/api-framework/node_modules/express/lib/router/index.js:521:19)\n at OpenApiValidator.installOperationHandlers (/Users/keshashah/work/api-framework/node_modules/express-openapi-validator/src/openapi.validator.ts:314:37)\n at /Users/keshashah/work/api-framework/node_modules/express-openapi-validator/src/openapi.validator.ts:215:30\n at processTicksAndRejections (internal/process/task_queues.js:95:5)","timestamp":"2023-05-18T06:02:49.057Z","type":"app-log"}

Expected behavior
It should return JSON or any expected response.

Examples and context
This bug got created because

express-openapi-validator/src/resolvers.ts

Line 38 in 01950b7

const handler = tmpModules[modulePath][oId] || tmpModules[modulePath].default;

here if tmpModules[modulePath][oId] does not exist then it should first check handler from tmpModules[modulePath].default[oId] if that does not exist then only return tmpModules[modulePath].default

Is there any specific reason for this? or should I create a PR for this.
Currently all our function with exports.default with operationId are not working with this upgrade.

[kesha-shah]

Proposed PR : #846