Add ability to respond to webhooks.

[Half-Shot]

Fixes #837

This adds two new features to the generic webhook connection type:

• The ability to set a response value for webhooks.
• The ability for connections to choose whether to block on the webhook function before responding.

[Twi1ightSparkle]

Hookshot is posting the message twice to Matrix when Wait for webhook function to complete before responding is checked. But looks to be sending the correct data back.

Testing what webhook settings duplicates messages

const responseBody = `
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
<soapenv:Body>
<notificationsResponse xmlns="http://soap.sforce.com/2005/09/outbound">
<Ack>true</Ack>
</notificationsResponse>
</soapenv:Body>
</soapenv:Envelope>
`.trim();

result = {
    empty: false,
    msgtype: 'm.text',
    plain: message,
    version: 'v2',
    webhookResponse: {
        body: responseBody,
        contentType: 'application/xml',
        statusCode: 418,
    }
};

---

Also, Wait for webhook function to complete before responding unchecks itself when you close and re-open the webhook in the configurator.

---

Waiting for my contact to do an actual test with Salesforce.

[Twi1ightSparkle]

Actually, once you have enabled Wait for webhook function to complete before responding., you can't turn it off again. It appears to just not read waitForComplete": true from the "uk.half-shot.matrix-hookshot.generic.hook", state event when opening the webhook

[Twi1ightSparkle]

Has now been tested with Salesforce, and Sf is happy 🎉