feat(cmakev2): Add uf2 target support for cmakev2

This commit adds support for uf2 targets for cmake2. The following
changes have been made:
- Adds a new tools/cmakev2/uf2.cmake.
- Adds the idf_create_uf2() function to create the uf2 targets. This
  function now takes the executable as an argument thus allowing the uf2
  target to be created per-executable.
- idf_project_default() is updated to create the uf2 targets.

tools/cmakev2/project.cmake

@@ -773,6 +773,12 @@ macro(idf_project_default)
 
     idf_create_save_defconfig()
 
+    idf_create_uf2("${executable}"
+                   TARGET uf2)
+    idf_create_uf2("${executable}"
+                   TARGET uf2-app
+                   APP_ONLY)
+
     idf_build_generate_metadata("${executable}")
 
     unset(build_dir)