[Docs] Fix broken multi-line installation commands and streamline prerequisites in Observability lab e1 #279

Current State

In Exercise 1 (Installing Prometheus and Grafana - e1/_index.md) of the Introduction to Observability learning path, several manual installation commands are broken across lines without line-continuation backslashes, causing terminal execution failures and 404 errors for learners:

1. Broken Prometheus Download (Lines 14–16):
   The download command splits the word prometheus across 3 lines:

   $ cd /tmp
   $ curl -LO
   https://github.com/prometheus/prometheus/releases/download/v2.49.1/pr
   ometheus-2.49.1.linux-amd64.tar.gz

   • curl -LO fails with curl: (2) no URL specified.
   • The middle line queries .../releases/download/v2.49.1/pr resulting in a 404 Not Found.
   • The trailing line triggers bash: ometheus-2.49.1.linux-amd64.tar.gz: command not found.
   • Consequently, the subsequent tar xvf prometheus-2.49.1.linux-amd64.tar.gz fails with Cannot open: No such file or directory.

2. Broken Grafana Setup Commands (Lines 114–121):

   $ sudo apt-get install -y apt-transport-https
   software-properties-common wget
   $ sudo mkdir -p /etc/apt/keyrings/
   wget -q -O - https://apt.grafana.com/gpg.key | gpg --dearmor | sudo
   tee /etc/apt/keyrings/grafana.gpg > /dev/null
   $ echo "deb [signed-by=/etc/apt/keyrings/grafana.gpg] https://apt.grafana.com
   stable main" | sudo tee -a /etc/apt/sources.list.d/grafana.list

   • software-properties-common wget is isolated on a new line and fails with command not found.
   • The pipe before tee is split across lines.
   • The multi-line echo string breaks quotation syntax and hangs the terminal.

3. Maintenance Debt & Outdated Version Pinning:
   The lab attempts to maintain 190+ lines of brittle OS-specific systemd service scripts, raw terminal output dumps, and hardcodes older versions (v2.49.1, v10.3.3).

Screenshots / Logs

Error 1: Broken Prometheus Download (Step 1)

1. Lab UI (Step 1 Broken Multi-line Command):

2. Terminal Execution Error (curl / tar failure):

3. GitHub Release Page (404 Not Found):

Error 2: Broken Grafana Setup (Step 10)

1. Lab UI (Step 10 Broken Package & Repo Command):

2. Terminal Execution Error (software-properties / echo hang):

Desired State

• Shell commands should be valid and runnable without syntax errors.
• In accordance with community architectural guidelines on reducing learning material fragility (established in [Docs] Fix broken Podman static binary download URL and command syntax in lab e5 #275 / [Docs] Fix broken multi-line installation commands and streamline prerequisites in lab e6 #277), third-party tool installation should be framed as external prerequisites pointing directly to official documentation (Prometheus and Grafana).
• The lab should streamline directly into the core hands-on objectives: connecting Prometheus as a Data Source in Grafana and creating metric visualization dashboards.

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