docs(autoware_pyplot): add missing readme and move the package to com…

…mon (#9546)

common/autoware_pyplot/README.md

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+# autoware_pyplot
+
+This package provides C++ interface for the notable `matplotlib` using `pybind11` backend for
+
+- creating scientific plots and images illustrating the function inputs/outputs
+- debugging the output and internal data of a function before unit testing in a more lightweight manner than planning_simulator
+
+## usage
+
+In your main function, setup the python context and import `matplotlib`
+
+```cpp
+#include <autoware/pyplot/pyplot.hpp>
+#include <pybind11/embed.h>
+
+// in main...
+  py::scoped_interpreter guard{};
+  auto plt = autoware::pyplot::import();
+```
+
+Then you can use major functionalities of `matplotlib` almost in the same way as native python code.
+
+```cpp
+{
+    plt.plot(Args(std::vector<int>({1, 3, 2, 4})), Kwargs("color"_a = "blue", "linewidth"_a = 1.0));
+    plt.xlabel(Args("x-title"));
+    plt.ylabel(Args("y-title"));
+    plt.title(Args("title"));
+    plt.xlim(Args(0, 5));
+    plt.ylim(Args(0, 5));
+    plt.grid(Args(true));
+    plt.savefig(Args("test_single_plot.png"));
+}
+
+{
+    auto [fig, axes] = plt.subplots(1, 2);
+    auto & ax1 = axes[0];
+    auto & ax2 = axes[1];
+
+    ax1.set_aspect(Args("equal"));
+    ax2.set_aspect(Args("equal"));
+}
+```