Consider re-enabling the redirector use @ download.moodle.org for plugins

Some history:

• With MDLSITE-2259 we activated plorg to start generating download URLs pointing to dlorg's redirector (it is a simple setting controlling them).
• Then, it was detected that mdeploy.php was not supporting those redirection responses coming from the redirector (MDL-39664). So immediately we switched back the old urls pointing to plorg.
• MDL-39664, before release, has fixed that behavior in 25_STABLE and master and also there is a backport request of it to 24_STABLE (MDL-39668).

So, right now:

• All 25_STABLE and master sites are supporting redirects in mdeploy.php
• Not all 24_STABLE sites are supporting redirects in mdeploy.php (Only when MDL-39668 is integrated and sites are upgraded redirects will be supported).
• There is not mdeploy.php in 23_STABLE

Luckily, for each Moodle release, we create a new "downloads/plugins API" @ download.moodle.org (see private https://github.com/moodlehq/serverscripts/tree/master/download.moodle.org/updates_api). Hence, 1.0 is for 23_STABLE sites, 1.1 is for 24_STABLE sites and 1.2 is for 25_STABLE/master sites.

So, it would be possible to:

1) Create a new 1.1.1 api (for 24_STABLE sites upgraded with MDL-39668 implemented). Just a duplication of current 1.1 api.
2) Hack the 1.1 api (non upgraded 24_SITES) with a simple str_replace(), so we ensure that any URL pointing to the dlorg redirector is changed back to plorg URLs before returning it to the site.
3) Re-enable in plorg the generation of redirector URLs. Upgraded sites will use the api 1.1.1, returning supported redirector urls. And non upgraded sites will use the hacked api 1.1, returning always plorg urls.

And that's the idea, it would allow us start using the redirector today for all sites and continue advancing on its features. Else we won't be able to re-enable it until 2.4 is out of support (1y delay!).

Comments welcome, ciao