fix(graphql): Change config from raw path to file: url

[6TELOIV]

What?

On windows, the payload-graphql generate:schema command fails.

Why?

Because the config it's trying to load is c:\path\to\config.js, which node interprets as \path\to\config.js on the c: protocol.

How?

By changing it to use a file URL, as in file:\\\c:\path\to\config.js. The change is the same as what the main payload cli does: https://github.com/payloadcms/payload/blob/main/packages/payload/src/bin/index.ts#L54

Fixes #9309

[6TELOIV]

Not sure how to write a regression test for this, as it's platform specific.

Could involve modifying findConfig instead to do this change (i.e, call pathToFileURL before returning) as the findConfig function only seems to be called in the 2 CLIs (payload-graphql and payload), and then modifying those usages to use the path directly. Or, maybe introduce a new function findConfigFileURL and have it wrap the findConfig function. With either of those changes, then this could have an integration test.