Inspect 'require' usage in lodestar

[twoeths]

Describe the bug

After esm migration, we can not use require function any more, otherwise we'll get error like below:

Aug-05 11:12:05.423[API]             ^[[31merror^[[39m: Req req-4b writeHeapdump error  NodeJS only
Error: NodeJS only
    at Object.writeHeapdump (file:///usr/src/lodestar/packages/beacon-node/src/api/impl/lodestar/index.ts:48:48)
    at Object.handler (file:///usr/src/lodestar/packages/api/src/utils/server/genericJsonServer.ts:39:41)
    at preHandlerCallback (/usr/src/lodestar/node_modules/fastify/lib/handleRequest.js:124:28)
    at preValidationCallback (/usr/src/lodestar/node_modules/fastify/lib/handleRequest.js:107:5)
    at handler (/usr/src/lodestar/node_modules/fastify/lib/handleRequest.js:70:7)
    at handleRequest (/usr/src/lodestar/node_modules/fastify/lib/handleRequest.js:30:9)
    at runPreParsing (/usr/src/lodestar/node_modules/fastify/lib/route.js:422:5)
    at next (/usr/src/lodestar/node_modules/fastify/lib/hooks.js:158:7)
    at handleResolve (/usr/src/lodestar/node_modules/fastify/lib/hooks.js:175:5)

Expected behavior

No error

Steps to Reproduce

curl -X POST http://localhost:9596/eth/v1/lodestar/writeheapdump