Add the Live Tennis plugin

Live tennis scores on a key: both players' surnames, the set score, the points
in the current game, a marker beside the server and a marker on the side
holding a break point. ATP, WTA, Challenger, ITF and juniors.

Complementary to SportsScores rather than competing with it: that plugin
covers the US leagues and soccer and has no tennis, this one has nothing but
tennis.

Data comes from the Live Tennis API, which the plugin author operates; the
plugin needs a key, and a free key covers everything it does. Both endpoints
it uses are on the free tier. The free tier allows 100 requests a day, so the
plugin defaults to a 15-minute refresh (96 requests a day) with 15 minutes as
a hard floor clamped in code, and every key showing tennis shares one cached
request.

The hash is the plugin repo's commit; entry follows the live shape in this
file rather than the 'commits' map still shown in the submission docs.

Author: bensynapse

Plugins.json

@@ -290,5 +290,9 @@
   {
     "url": "https://github.com/larkum/StreamController-SpeedtestPlus",
     "hash": "f2aa82563fa53997f9c2be26c316daf3f35d1ce0"
+  },
+  {
+    "url": "https://github.com/bensynapse/StreamController-LiveTennis",
+    "hash": "REPLACE_WITH_PLUGIN_COMMIT_SHA"
   }
 ]