[FEATURE] Set up GitHub Pages for Observability Stack documentation

[anirudha]

Is your feature request related to a problem?

As the project matures, there is no documentation site for users and contributors to reference. We need a proper GitHub Pages site to publish component docs, user guides, and version mapping — kept current with each code release.

What solution would you like?

Enable GitHub Pages for the repo with a static site generator (e.g. MkDocs with Material theme or Jekyll). The site should include:

• Getting Started: Installation, quickstart, prerequisites
• Components: OpenSearch, Data Prepper, OTel Collector, Prometheus, OpenSearch Dashboards — what each does and how it's configured in the stack
• User Guide: Configuration options, enabling examples, enabling OTel Demo, custom instrumentation, Helm deployment
• Architecture: Stack topology, data flow, networking
• Version Mapping: Table mapping each Observability Stack release version to the specific component versions (OpenSearch, Data Prepper, OTel Collector, Prometheus, etc.). The stack version is independent of individual component versions.
• Contributing: Link back to CONTRIBUTING.md

Example version mapping table:

Stack Version	OpenSearch	Data Prepper	OTel Collector	Prometheus	Dashboards
1.0.0	2.x.x	2.x.x	0.x.x	2.x.x	2.x.x

Implementation:

• Source docs from a docs/ directory in the repo
• GitHub Actions workflow to build and deploy on push to main or on release tags
• Support versioned documentation tied to stack releases

What alternatives have you considered?

• Keeping docs only in-repo as markdown files (doesn't scale, not user-friendly)
• External hosted docs (adds operational overhead outside the project)

Do you have any additional context?

Acceptance criteria:

• GitHub Pages site is live and accessible
• Docs cover all sections listed above
• Version mapping table is present and accurate for the current release
• CI workflow auto-deploys docs on merge to main
• Docs are reviewable via PR (source lives in repo)