Prepare 3.10.0-beta release (#313)

This diff implements part of the release checklist at https://github.com/ooni/probe/issues/1439. The plan is to bless a beta release and use it for further testing on Android devices. Afterward, we need to apply some extra changes to the `cli` (including https://github.com/ooni/probe-cli/pull/314 and https://github.com/ooni/probe-cli/pull/312). Finally, we will bless a full 3.10.0 release.

internal/engine/ooapi/swagger_test.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// 2021-03-31 16:50:07.052341608 +0200 CEST m=+0.000586077
+// 2021-04-26 14:35:22.20867232 +0200 CEST m=+0.000560530
 
 package ooapi
 
@@ -9,7 +9,7 @@ const swagger = `{
     "swagger": "2.0",
     "info": {
         "title": "OONI API specification",
-        "version": "0.20210331.3145007"
+        "version": "0.20210426.4123522"
     },
     "host": "api.ooni.io",
     "basePath": "/",