parsing  headers as integer  cause failed to send usage report to apollo studio
### Issue Description

when sending all headers to apollo studio 
```ts
ApolloServerPluginUsageReporting({
      sendHeaders: { all: true },
      sendVariableValues: { all: true },
    }),
```
apollo server parse some of the request headers value to integer(I only observed field `content-length` parsed to an integer, not sure if  other fields are also able to convert to non-string value),
headers below are the values we observed in [code line ](https://github.com/apollographql/apollo-server/blob/8cdbd14d17665ab430cc5f24bc90e60084ff0ce7/packages/server/src/plugin/usageReporting/plugin.ts#L712) during debugging
```json
{
  "requestHeaders": {
    "host": {
      "value": [
        "localhost:4001"
      ]
    },
    "connection": {
      "value": [
        "keep-alive"
      ]
    },
    "content-length": {
      "value": [
        227
      ]
    }
  }
...
}
```

 but usage report's proto-buf defined the header value as string

```proto
message Values map<string, Values> request_headers = 4;{
      repeated string value = 1;
    }
...
map<string, Values> request_headers = 4;
```
so we get the errors as bellow:
```
2023-01-08T15:19:27.472Z	xxxx 	ERROR	Error: Error encoding trace: http.requestHeaders.value: string[] expected
    at addTrace (/var/task/node_modules/@apollo/server/dist/cjs/plugin/usageReporting/plugin.js:395:35)
    at runNextTicks (node:internal/process/task_queues:61:5)
    at processImmediate (node:internal/timers:437:9)
    at process.callbackTrampoline (node:internal/async_hooks:130:17)

-- | --
```



### Link to Reproduction

https://github.com/Blankll/serverless-event

### Reproduction Steps

follow the repo's readme to package & deploy it to aws, checke the cloudwatch you will see the error message