feat(self-signed): expose days option

@xen-orchestra/self-signed/README.md

@@ -19,7 +19,14 @@ Installation of the [npm package](https://npmjs.org/package/@xen-orchestra/self-
 ```js
 import { genSelfSigned } from '@xen-orchestra/self-signed'
 
-console.log(await genSelfSigned())
+console.log(
+  await genSelfSigned({
+    // Number of days this certificate will be valid.
+    //
+    // Default: 360
+    days: 600,
+  })
+)
 // {
 //   cert: '-----BEGIN CERTIFICATE-----\n' +
 //     // content…

@xen-orchestra/self-signed/USAGE.md

@@ -1,7 +1,14 @@
 ```js
 import { genSelfSigned } from '@xen-orchestra/self-signed'
 
-console.log(await genSelfSigned())
+console.log(
+  await genSelfSigned({
+    // Number of days this certificate will be valid.
+    //
+    // Default: 360
+    days: 600,
+  })
+)
 // {
 //   cert: '-----BEGIN CERTIFICATE-----\n' +
 //     // content…

@xen-orchestra/self-signed/index.js

@@ -10,12 +10,12 @@ const openssl = (cmd, args, { input, ...opts } = {}) =>
     }
   })
 
-exports.genSelfSignedCert = async () => {
+exports.genSelfSignedCert = async ({ days = 360 } = {}) => {
   const key = await openssl('genrsa', ['2048'])
   return {
     cert: await openssl(
       'req',
-      ['-batch', '-new', '-key', '-', '-x509', '-days', '360', '-nodes'],
+      ['-batch', '-new', '-key', '-', '-x509', '-days', String(days), '-nodes'],
       {
         input: key,
       }