Allow passing JavaScript code directly to `plugins` in `codegen.ts`

### Is your feature request related to a problem? Please describe.

No.

### Describe the solution you'd like

Currently, the `plugins` field only accepts npm packages, workspace packages, or external files via relative paths. However, I’d like to request support for passing JavaScript code directly, as shown below:

Current:
```typescript
const config: CodegenConfig = {
schema: [
'./**/*.graphql',
],
generates: {
'./example.ts': {
plugins: [
{
'./example-plugin.ts': {
name: 'John',
},
// OR
'@myworkspace/example-plugin': {
name: 'John',
},
},
],
},
},
}
```

Desired:
```typescript
const examplePlugin = (config) => {
plugin: async (schema, documents, config, info) => {
return `Hello, ${config.name}`
},
validate: (schema, documents, config, outputFile, allPlugins, pluginContext) => {
throw new Error('Something went wrong...')
},
}

const config: CodegenConfig = {
schema: [
'./**/*.graphql',
],
generates: {
'./example.ts': {
plugins: [
examplePlugin({
name: 'John',
}),
],
},
},
}
```

For reference, this is possible in `esbuild.config.ts`, allowing small plugins to be written directly within the configuration file, which is very convenient.

```typescript
import { type Plugin, build } from 'esbuild'

const examplePlugin = (config): Plugin => {
return {
name: 'examplePlugin',
setup: (build) => {
console.log(`Hello, ${config.name}`)
}
}
}

build({
plugins: [
examplePlugin({
name: 'John',
}),
],
})
```

### Describe alternatives you've considered

_No response_

### Any additional important details?

_No response_