Rename server.js file to server.mjs

[aarbi]

This is already referenced in tsconfig.node.json here
also the current node LTS version supports running .mjs scripts

[brookslybrand]

@aarbi can you help me understand the benefit here?

I'm definitely with you that the tsconfig.node.json file should match whatever is being used, but not sure the advantage of merging this otherwise

[aarbi]

Either ways are fine with me too.
server.js is syntactically a valid .mjs file. We also have type = module in package.json. So just so everything would esm compatible.
Otherwise I can update this PR to only update the tsconfig file