split: convert example tests into datadriven

There were existing example tests for evaluating the load based splitter. These
were not a part of testing but instead could be run ad-hoc for
experiments. This commit updates these tests to be datadriven in order
to spot regressions easily in the load based splitter. The datadriven
interface may also be used for experimental evaluation in an ad-hoc
manner, similar to before.

Release note: None

pkg/kv/kvserver/split/BUILD.bazel

@@ -31,16 +31,20 @@ go_test(
         "weighted_finder_test.go",
     ],
     args = ["-test.timeout=55s"],
+    data = glob(["testdata/**"]),
     embed = [":split"],
     deps = [
         "//pkg/keys",
         "//pkg/roachpb",
+        "//pkg/testutils/datapathutils",
+        "//pkg/testutils/skip",
         "//pkg/util/encoding",
         "//pkg/util/leaktest",
         "//pkg/util/metric",
         "//pkg/util/stop",
         "//pkg/util/timeutil",
         "//pkg/workload/ycsb",
+        "@com_github_cockroachdb_datadriven//:datadriven",
         "@com_github_stretchr_testify//assert",
         "@com_github_stretchr_testify//require",
         "@org_golang_x_exp//rand",