chore: Moved to .envrc.example file.

[toastdriven]

🎯 What needed to be done and why?

(Partially) Resolves #221

There will be follow-up PRs doing similar things in both scaf-fullstack-template & scaf-aws-lambda-app-template.

Quick summary of the issue

This relocates the .envrc file to .envrc.example (& ignores .envrc). This allows developers to customize a local version without accidentally checking changes into VCS.

🆕 What is changed by this PR?

• Created an generic .envrc.example based on the existing .envrc
• Added a git ignore for .envrc
• Added to the README telling developers to copy the file

📋 Code Review Cheatsheet

What the reviewer should check

Check	Description
🚚 Diff size	Is the PR small and focused, or should it be broken into smaller PRs?
🧪 Unit tests	Are new features covered with appropriate unit tests?
🥼 Acceptance Criteria met	Are the Acceptance Criteria listed in the issue met?
🧐 Code clarity	Is the code easy to understand? Are variable and function names meaningful?
🧩 Code organization	Are files, modules, and functions structured logically?
🪚 Conciseness	Is the code free of unnecessary complexity or redundant code?
💬 Comments & documentation	Are code comments explaining why and not how? Is the documentation up-to-date?
🧮 Code consistency	Does the code follow existing patterns and conventions in the project?
☣️ Function length	Are functions too long? Should they be broken into smaller, more focused functions?
☢️ Class design	Are classes well-structured and not overly large or doing too much?
🐾 Logging and debugging statements	Are print/debug statements removed or replaced with proper logging?