[Web hooks] Ability to wait for pre-hook response

[pdonias]

See xoa-support#2390

Whether or not the hook awaits should be configurable.
Timeout if it never gets a response.

[julien-f]

1. adding a new boolean setting:

   xen-orchestra/packages/xo-server-web-hooks/src/index.js

   Lines 118 to 138 in 24b264b

   	method: {
   	description: 'The method to be bound to',
   	enum: Object.keys(apiMethods).sort(),
   	title: 'Method',
   	type: 'string',
   	},
   	type: {
   	description:
   	'Right before the API call *or* right after the action has been completed',
   	enum: ['pre', 'post', 'pre/post'],
   	title: 'Type',
   	type: 'string',
   	},
   	url: {
   	description: 'The full URL you wish the request to be sent to',
   	// It would be more convenient to configure 1 URL for multiple
   	// triggers but the UI implementation is not ideal for such a deep
   	// configuration schema: https://i.imgur.com/CpvAwPM.png
   	title: 'URL',
   	type: 'string',
   	},

2. only returns promise if waitHookResponse:

   xen-orchestra/packages/xo-server-web-hooks/src/index.js

   Lines 10 to 16 in 24b264b

   	this._makeRequest(url, type, data).catch(error => {
   	log.error('web hook failed', {
   	error,
   	webHook: { ...data, url, type },
   	})
   	})
   	)

3. replace by await emitAsync(xo, 'xo:preCall', data):

   xen-orchestra/packages/xo-server/src/xo-mixins/api.js

   Line 272 in 24b264b

   xo.emit('xo:preCall', data)

4. maybe we should do the same for postCall