Evaluate new Plex update API

[demonbane]

Just a placeholder to review the new update API that PMS uses internally. Info from one of the Plex devs on the forums:

Note: If you only want to check for updates for a specific build/distro you can use this endpoint

https://plex.tv/updater/products/5/check.xml?build=linux-x86_64&channel=8&distribution=debian&X-Plex-Token=REDACTED

And for public:

You can use channel=16 for public on the https://plex.tv/downloads/latest/5 and https://plex.tv/updater/products/5/check.xml endpoints.

The only catch is that I haven't found a way to specify which version to download specifically, you just get "latest". While that may be what we want, I'd prefer to be able to actually specify the version each time so that there are no surprises.

[demonbane]

Sample output from the new endpoint:

<?xml version="1.0" encoding="UTF-8"?>
<MediaContainer friendlyName="myPlex" identifier="com.plexapp.plugins.myplex" machineIdentifier="d263492a105fa6d0656e133da62430fdf0f117f1" size="1" title="Updates">
  <Release id="2649" version="1.15.0.659-9311f93fd" added="- (Linux) Support for Ubuntu/Debian ARMv7 and ARMv8 platforms.&#13;&#10;- (NAS) Support for ASUSTOR, QNAP, and Synology ARMv8 devices.&#13;&#10;- (NAS) Support for hardware encoding on QNAP Intel/AMD 64-bit devices with a discrete Nvidia GPU.&#13;&#10;- (NAS) Support for volume selection, and app migration on QNAP devices." fixed="- (DVR) Avoid a few crashes around parsing bad JSON from OnConnect (#8889)&#13;&#10;- (DVR) Avoid caching EPG HTTP cache requests for longer than the refresh time (#9629)&#13;&#10;- (DVR) Avoid downloading XMLTV files to disk before parsing (#9272)&#13;&#10;- (DVR) Certain scheduled recordings would incorrectly show an error (#9325)&#13;&#10;- (DVR) Change the way Plex Tuner Service returns keys for TVButler devices, especially on macOS, to properly handle using multiple TVButlers on the same system. N.B. This is a breaking change for users of TVButler devices. Those users will need to delete and recreate their DVR to use the new device information. (#8760)&#13;&#10;- (DVR) Disk space checking underestimates the necessary amount of space when starting recordings (#8807)&#13;&#10;- (DVR) Ensure grab operations get destroyed after a tune fails (#9465)&#13;&#10;- (DVR) Fixed a bug where changing recording priority would not update the schedule. (#9035)&#13;&#10;- (DVR) Log which device we're allocating a tuner from&#13;&#10;- (DVR) Output signal strength/quality information into log periodically during tunes (#9503)&#13;&#10;- (DVR) Plex Tuner Service now properly detects when a transcode session exited due to signal failure and releases the tuner (#9174)&#13;&#10;- (DVR) Revert timeout changes, should help with timeouts during tune startup (#9473)&#13;&#10;- (DVR) Translate Guide header for clients to display (#8698)&#13;&#10;- (Library) Library summary endpoint should report the correct duration for large music libraries (#9223)&#13;&#10;- (Live TV) Fix for intermittent tune failures. (#9412)&#13;&#10;- (Live) Avoid delaying video playback while leading audio plays (#9343)&#13;&#10;- (Music) Restricting music libraries with labels could prevent them from loading. (#8935)&#13;&#10;- (Scanner) Add support for reading Opus metadata (#5974)&#13;&#10;- Corrected rare crash involving accessing User data (#9464)&#13;&#10;- The server could crash when TV media was being deleted. (#9350)&#13;&#10;- Updated translations" live="true" autoupdate="true" createdAt="2019-02-07 14:36:54 UTC">
  </Release>
</MediaContainer>