docs(sim): add Try PX4 quick-start and pre-built packages reference (#26957)

Adds documentation for the SITL containers and .deb packages introduced in #26495. The containers are now live on Docker Hub: [`px4io/px4-sitl:latest`](https://hub.docker.com/r/px4io/px4-sitl) and [`px4io/px4-sitl-gazebo:latest`](https://hub.docker.com/r/px4io/px4-sitl-gazebo).

The main addition is a [Try PX4 Simulation](https://docs.px4.io/main/en/dev_setup/try_px4) page that leads with a single `docker run` command and gets someone flying in under a minute. It lives in Getting Started, right after Recommended Hardware/Setup, so it's one of the first things new users see.

The existing `.deb` package reference has been moved from `packaging/px4_sitl_deb.md` to `simulation/px4_sitl.md` and expanded to cover both containers and `.deb` packages on one page. Sections are ordered by how people use them: what's available, install, configure, connect QGC/MAVSDK, connect ROS 2.

Other changes:
- README now has a "Try PX4" section with the docker one-liner above "Build from Source"
- Landing page (`index.md`) reworked to lead with "Try PX4" before "For Developers"
- Toolchain page (`dev_env.md`) gets a tip redirecting simulation-only users to pre-built packages
- `getting_started.md` and `SUMMARY.md` updated with links to the new pages
- Simulation index tip updated to mention containers alongside `.deb` packages

The SIH container image is published as `px4io/px4-sitl` (renamed from `px4io/px4-sitl-sih`) so the default lightweight option carries the simplest name. The Gazebo image remains `px4io/px4-sitl-gazebo`.

Also upgrades all GitHub Actions in the SITL workflow to Node.js 24 compatible versions (`actions/checkout@v6`, `actions/cache@v5`, `actions/upload-artifact@v7`, `actions/download-artifact@v8`, `docker/setup-buildx-action@v4`, `docker/build-push-action@v7`) to fix the Node.js 20 deprecation warning ahead of the June 2026 deadline.

---------

Signed-off-by: Ramon Roche <mrpollo@gmail.com>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>

.github/workflows/build_deb_package.yml

@@ -40,7 +40,7 @@ jobs:
       should_push: ${{ steps.push.outputs.should_push }}
     steps:
       - uses: runs-on/action@v2
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-tags: true
           submodules: false
@@ -93,7 +93,7 @@ jobs:
           apt-get update && apt-get install -y git
           git config --global --add safe.directory $(realpath .)
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           fetch-tags: true
@@ -103,7 +103,7 @@ jobs:
         run: ./Tools/ci/use_aws_apt_mirror.sh
 
       - name: Cache apt packages
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: /var/cache/apt/archives
           key: apt-${{ matrix.target }}-${{ matrix.codename }}-${{ matrix.arch }}-${{ hashFiles('Tools/setup/ubuntu.sh') }}
@@ -136,7 +136,7 @@ jobs:
           - { image: gazebo, repo: px4-sitl-gazebo, target: default, arch: arm64, runner: arm64, platform: "linux/arm64", dockerfile: Dockerfile.gazebo }
     steps:
       - uses: runs-on/action@v2
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: false
           fetch-depth: 1