Add EDOT mentions on landing pages

[alexandra5000]

This PR adds mentions of EDOT as the recommended/preferred option across Observability docs, normalizing EDOT as the preferred approach while preserving existing content.

• Added EDOT recommendations: tips/notes in infrastructure, logs, APM, and CI/CD docs recommending EDOT Collector or EDOT SDKs as the preferred way to collect telemetry data
• Updated placeholders: uses {{edot}} substitute where appropriate
• Fixed linting errors: added missing applies_to tags and corrected invalid lifecycle values (all)

Part of #82

Closes #110

LLM usage disclosure: I prompted Claude 4.5 Sonnet in Cursor to find instances where EDOT mentions are missing (according to the issue description and internal conversations about this audit), then reviewed the content manually and fixed Vale linting issues.

[github-actions]

🔍 Preview links for changed docs

• solutions/observability/apm/index.md
• solutions/observability/cicd.md
• solutions/observability/infra-and-hosts.md
• solutions/observability/infra-and-hosts/analyze-infrastructure-host-metrics.md
• solutions/observability/logs/ecs-formatted-application-logs.md
• solutions/observability/logs/plaintext-application-logs.md

[benironside]

Nice work. Left some suggestions, I hope they're helpful. Thanks!

[github-actions]

Vale Linting Results

Summary: 3 suggestions found

💡 Suggestions (3)

File	Line	Rule	Message
solutions/observability/logs/ecs-formatted-application-logs.md	15	Elastic.WordChoice	Consider using 'efficiently' instead of 'easily', unless the term is in the UI.
solutions/observability/logs/ecs-formatted-application-logs.md	18	Elastic.Acronyms	'ECS' has no definition.
solutions/observability/logs/ecs-formatted-application-logs.md	18	Elastic.Acronyms	'ECS' has no definition.

[florent-leborgne]

LGTM