Fix over-linking issues in web exporter documentation

What does this MR do and why?

This MR addresses over-linking issues in the web exporter documentation that were disrupting reading flow and violating GitLab documentation standards.

Problems identified:

• Flow-disrupting parenthetical links: Mid-sentence links that break reading flow
• Overwhelming procedural links: Nearly every task step contained multiple links
• Multiple links per sentence: Complex sentences with multiple concepts linked

Changes made:

🔴 High Priority Fixes:

1. Removed flow-disrupting parenthetical links:

   • Removed inline Puma link that was explanatory but not essential
   • Removed mid-sentence Docker links that interrupted reading flow

2. Consolidated procedural links into "Related topics" sections:

   • Moved Prometheus configuration links out of task steps
   • Created dedicated "Related topics" sections after major procedures
   • Kept only essential reconfigure GitLab link in task steps

3. Simplified task steps:

   • Step 1: Removed link to "Enable Prometheus" (should be prerequisite knowledge)
   • Step 3: Removed three inline links, moved to Related topics
   • Troubleshooting: Moved Docker links to Related topics section

🟡 Medium Priority Fixes:

4. Restructured multiple links per sentence:
   • Simplified complex sentences in the "How GitLab metrics collection works" section
   • Broke down explanatory text to reduce cognitive load

Impact:

• Link density reduced from 6/10 to approximately 3/10
• Improved task flow: Users can complete procedures without link distractions
• Better readability: Cleaner sentences with fewer interruptions
• Maintained navigation: All important links preserved in Related topics sections

Compliance with GitLab standards:

• ✅ Follows guideline to "avoid multiple links in a single task"
• ✅ Reduces cognitive load as recommended in style guide
• ✅ Uses "Related topics" pattern for supplementary information
• ✅ Maintains descriptive link text standards
• ✅ Preserves all necessary navigation paths

Screenshots or screen recordings

Before:

• Task steps contained 3+ links each
• Mid-sentence parenthetical links disrupted flow
• Complex sentences with multiple linked concepts

After:

• Clean task steps focused on actions
• Links organized in Related topics sections
• Simplified explanatory text

How to set up and validate locally

1. Review the updated documentation at doc/administration/monitoring/prometheus/web_exporter.md
2. Verify that:
   • Task procedures are easier to follow
   • Related topics sections provide necessary navigation
   • Reading flow is improved without losing essential information

MR acceptance checklist

• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guidelines
• Separation of EE specific content