Add generate-debug-config.py to tools directory

[ben-taussig-solo]

Description

• Adds a modified version of upstream's generate_debug_config.py script to the /tools directory. This script can be used to generate vscode/gdb debug configuration for an individual test target.
  • This script can be used to work around strange debugger behavior discussed in solo's "Setting up Ubuntu for Envoy dev" slab guide
• More specifically, the script:
  • compiles the test target and a dwarf package file (.dwp) with debug symbols, as described in the envoy gdb guide here: https://github.com/envoyproxy/envoy/blob/main/bazel/README.md#running-a-single-bazel-test-under-gdb
  • updates the user's .vscode/launch.json to include a target that can be used to run the test under gdb
• The original script can be found at: https://github.com/envoyproxy/envoy/blob/main/tools/vscode/generate_debug_config.py
  • Currently, that script is not functional, primarily because it attempts to set launch.json config fields which do not exist, like debugger_args (should be miDebuggerArgs)
  • See here: https://github.com/envoyproxy/envoy/blob/main/tools/vscode/generate_debug_config.py#L66-L73
  • The primary changes introduced to the script with this PR correct those fields to point to legitimate launch.json config fields
    • documentation on vscode's launch.json C/C++ config can be found here: https://code.visualstudio.com/docs/cpp/launch-json-reference