[Builder] Plain-text Body doesnt work

### Helm Chart Version

airbyte-v2/2.0.19

### What step the error happened?

Other

### Relevant information

After upgrading to airbyte community 2.0, several existing SOAP builders broke (can't test them) because choosing "Plain-text Body" doesn't work

Can't confirm if the connections broke (I don't think so, or I'd be dead now 😓 )

Also, "plain-text" body being a simple input instead of textarea significantly worsened the XML request experience

---

## Steps to Reproduce
* create a new Custom Connector from scratch
* choose POST and any https://webhook.site/ to test
* tick "Request Body" and choose "Plain-text Body" (which now seems to be the only option to send XML requests)
* put any text (could be xml, or just "hi")
* see that it errors (is it expecting a json?)

Something went wrong in the connector. See the logs for more details.
Exception while syncing stream test_xml: Request body json cannot be a string

### Relevant log output

```shell
Something went wrong in the connector. See the logs for more details.
Exception while syncing stream test_xml: Request body json cannot be a string

Could not successfully make a request to the API. Check the logs for more information on this issue.
```