Add several elixir solutions

elixir/lucas-numbers/.exercism/config.json

@@ -0,0 +1,21 @@
+{
+  "authors": [
+    "neenjaw"
+  ],
+  "contributors": [
+    "angelikatyborska"
+  ],
+  "files": {
+    "solution": [
+      "lib/lucas_numbers.ex"
+    ],
+    "test": [
+      "test/lucas_numbers_test.exs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.ex"
+    ]
+  },
+  "language_versions": ">=1.10",
+  "blurb": "Learn about streams by generating the Lucas number sequence."
+}

elixir/lucas-numbers/.exercism/metadata.json

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+{"track":"elixir","exercise":"lucas-numbers","id":"843df89f0b464117ac83a3f4120e8404","url":"https://exercism.org/tracks/elixir/exercises/lucas-numbers","handle":"halfdan","is_requester":true,"auto_approve":false}