[tls] Add Rust binary to do the work of fish scripts

- Migrate get-cfssl-binaries.fish to Rust
- Use create_global_singleton! from r3bl_core
- Refactor script helper mod to be more bash-like
- scripting.rs:
  - Extract path, directory, environment, github_api, etc modules in scripting.rs
  - Make the code idiomatic Rust
  - Add tests to each module
- Path and PathBuf
  - Use Path instead of PathBuf where possible
  - Use impl AsRef<Path> to receive arguments for max generalization for calling code
  - Use &Path instead of &PathBuf
- Use TryFrom to implement conversion from OutputFolderLocations enum to PathBuf
- Add OS specific behaviors to scripting.rs

tls/.vscode/settings.json

@@ -1,5 +1,6 @@
 {
   "cSpell.words": [
+    "Bufs",
     "CFSSL",
     "cfssljson",
     "gencert",
@@ -11,6 +12,8 @@
     "pushd",
     "rcat",
     "realpath",
+    "replacen",
+    "reqwest",
     "rustls",
     "webpki"
   ]