DENG-2918-UDFs for URL parsing (#5141)

* DENG-2918-UDFs for URL parsing

* removing get_host because net.host() exists

sql/mozfun/utils/get_url_path/README.md

@@ -0,0 +1,4 @@
+This UDF extracts path from a URL string.
+
+The path is everything after the host and before parameters.
+This function returns "/" if there is no path.

sql/mozfun/utils/get_url_path/metadata.yaml

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+description: Extract the Path from a URL
+friendly_name: Get URL Path

sql/mozfun/utils/get_url_path/udf.sql

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+CREATE OR REPLACE FUNCTION utils.get_url_path(url STRING)
+RETURNS STRING AS (
+  "/" || COALESCE(
+    REGEXP_EXTRACT(REPLACE(REPLACE(url, "https://", ""), "http://", ""), r"\/([^&?#]*)"),
+    ""
+  )
+);
+
+-- Tests
+SELECT
+  mozfun.assert.equals("/path", utils.get_url_path("https://some-url.com/path")),
+  mozfun.assert.equals("/path", utils.get_url_path("http://some-url.com/path?more")),
+  mozfun.assert.equals("/path", utils.get_url_path("http://some-url.com/path#more")),
+  mozfun.assert.equals("/path", utils.get_url_path("http://some-url.com/path?more&utm=123")),
+  mozfun.assert.equals(
+    "/path/with/multiple/slashes",
+    utils.get_url_path("http://some-url.com/path/with/multiple/slashes?more")
+  ),
+  mozfun.assert.equals("/", utils.get_url_path("https://some-url.com")),
+  mozfun.assert.equals("/", utils.get_url_path("https://some-url.com/")),
+  mozfun.assert.equals("/path", utils.get_url_path("some-url.com/path"))