feat: add lua script to compare two k6-summary files

sbroad-cartridge/stress-test/README.md

 # Load testing
-
+## Using docker-compose
+Run from sbroad directory
+```
+make stress test=projection
+```
+Parameter `test` is type of stress test (corresponding to the name of folder). As result you will see file `k6_summary.lua` with summarized metrics inside chosen stress test folder.
+## Using k6 and tarantool
 1. Run [test application](../test_app)
     ```bash
     cd ../test_app && cartridge start
@@ -20,9 +26,28 @@
 
 1. Run the [k6](https://k6.io/docs/getting-started/running-k6/) script
     ```bash
-   ./k6 run -u 10 -d 1m k6.js
+   ./k6 run -u 10 -d 1m k6.js --summary-export k6_summary.json
    ```
-
-**Note:**
+   **Note:**
 If you run stress tests sequentially, you may need to do `cartridge clean` before next test run because tests might have
 conflicting schemas.
+
+## Compare results
+If you need to compare results serveral test, you may run
+```
+lua compare.lua path_to_k6_summary_1.json path_to_k6_summary_2.json
+```
+It considered that first result must have lower rps to get 0 exit code. Example of output:
+```
+$ lua compare.lua path_to_k6_summary_2.json path_to_k6_summary_1.json
++----------------+-----------------+------------------+
+| metrics        | left result     | right result     |
++----------------+-----------------+------------------+
+| Success value  | 0.3333689238811 | 0.33428112947271 |
+| Passes         | 71812           | 71244            |
+| Fails          | 143601          | 141882           |
+| VUs            | 10              | 10               |
+| Iterations rps | 3539.5409122402 | 3503.5619844057  |
++----------------+-----------------+------------------+
+Left (first) result must have lower or equal rps
+```

sbroad-cartridge/stress-test/compare.lua

+local json = require("json")
+
+local function print_comparison(file1, file2)
+    -- Get the column headers
+    local headers = {"metrics", "left result", "right result" }
+
+    -- Get the row data
+    local rows = {
+      {"Success value", file1.metrics.success.value, file2.metrics.success.value},
+      {"Passes", file1.metrics.success.passes, file2.metrics.success.passes},
+      {"Fails", file1.metrics.success.fails, file2.metrics.success.fails},
+      {"VUs", file1.metrics.vus.value, file2.metrics.vus.value},
+      {"Iterations rps", file1.metrics.iterations.rate, file2.metrics.iterations.rate}
+    }
+
+    -- Calculate the maximum length of each column
+    local max_lengths = {0, 0, 0}
+    for i, header in ipairs(headers) do
+      max_lengths[i] = #header
+    end
+    for _, row in ipairs(rows) do
+      for i, value in ipairs(row) do
+        max_lengths[i] = math.max(max_lengths[i], #tostring(value))
+      end
+    end
+
+    -- Print the table
+    local separator = "+" .. string.rep("-", max_lengths[1] + 2)
+      .. "+" .. string.rep("-", max_lengths[2] + 2)
+      .. "+" .. string.rep("-", max_lengths[3] + 2) .. "+"
+    print(separator)
+    for i, header in ipairs(headers) do
+      io.write("| " .. string.format("%-" .. max_lengths[i] .. "s", header) .. " ")
+    end
+    io.write("|\n")
+    print(separator)
+    for _, row in ipairs(rows) do
+      for i, value in ipairs(row) do
+        io.write("| " .. string.format("%-" .. max_lengths[i] .. "s", tostring(value)) .. " ")
+      end
+      io.write("|\n")
+    end
+    print(separator)
+  end
+
+local function load_file(file_path)
+    local f = assert(io.open(file_path, "r"))
+    local content = f:read("*all")
+    f:close()
+    return content
+end
+
+local function compare_iterations_rate(file_path1, file_path2)
+    local content1 = load_file(file_path1)
+    local content2 = load_file(file_path2)
+    local data1 = json.decode(content1)
+    local data2 = json.decode(content2)
+    local rate1 = data1.metrics.iterations.rate
+    local rate2 = data2.metrics.iterations.rate
+
+    print_comparison(data1, data2, file_path1, file_path2)
+    if rate1 >= rate2 then
+        print("Left (first) result must have lower or equal rps")
+        os.exit(1)
+    end
+    os.exit(0)
+end
+
+compare_iterations_rate(arg[1], arg[2])