Dev Container lock file and Dependabot configuration for devcontainers

[Copilot]

Thank you for helping make the Radius documentation better!

Please follow this checklist before submitting:

• Read the contribution guide
• Commands include options for Linux, MacOS, and Windows within codetabs
• New file and folder names are globally unique
• Page references use shortcodes instead of markdown or URL links
• Images use HTML style and have alternative text
• Places where multiple code/command options are given have codetabs

Description

Pins devcontainer feature versions for reproducible builds and adds Dependabot automation to keep them updated.

• .devcontainer/devcontainer.json: Updated feature references to use explicit version identifiers (e.g. git:1.3.5, go:1.3.3, hugo:1.1.3, node:1.7.1) so versions are visible and match the lock file 1:1
• .devcontainer/devcontainer-lock.json (new): Locks each feature to a specific version with SHA-256 integrity hash for reproducible environment builds. Feature keys use explicit version identifiers matching those in devcontainer.json
• .github/dependabot.yml: Adds devcontainers ecosystem entry targeting the edge branch with weekly updates — Dependabot will keep both devcontainer.json and devcontainer-lock.json in sync automatically

Issue reference

N/A — Proactive improvement to pin devcontainer feature versions and enable automated dependency updates.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[brooke-hamilton]

@copilot I think you need to update the dev container lock file identifiers too

[Copilot]

@copilot I think you need to update the dev container lock file identifiers too

Updated the lock file keys in commit 83d53e0. Both files now use matching explicit version identifiers (e.g. git:1.3.5, go:1.3.3, hugo:1.1.3, node:1.7.1).