Add Flagd-ui to demo docs

[maindotmarcell]

Changes

Changes required for the documentation concerning the flagd-ui feature.

As we have a ready PR for the first version of the flagd-ui, we would like to start thinking about how this new feature can be included in the documentation. Below you can find what I've implemented in this PR as my suggestions:

• Screenshots -> Add screenshots of the UI
• Docker deployment -> Add :8080/feature route
• Kubernetes deployment -> Add :8080/feature route
• Feature flags page -> Mention the possibility to toggle the flags through the UI
• Requirements/architecture -> mention under feature flagging section

As it is not directly a microservice of the astronomy shop app, but it is an instrumented service nonetheless, there a few where it might make sense to include it (the flagd service itself is currently not included in these):

• Architecture charts
• List of Services

Additionally it might make sense to create a separate docs page for this feature at some point.

Thank you in advance for reviewing! 🚀

Let me know if I missed anything :)

[svrnm]

Thank you, I commented with a few change requests

[maindotmarcell]

Thank you, I commented with a few change requests

@svrnm Thank you for the review, I've applied the suggested changes in the last commit

[svrnm]

Thank you, I commented with a few change requests

@svrnm Thank you for the review, I've applied the suggested changes in the last commit

thanks!

@open-telemetry/demo-approvers please take a look!

[julianocosta89]

LGTM, we just need to get the Helm chart PR merged before merging this one to avoid user's confusion.

Also, could you add the flagd-ui to the architecture page?
https://github.com/open-telemetry/opentelemetry.io/blob/main/content/en/docs/demo/architecture.md

I have it updated here if you would like: mermaid.live

[julianocosta89]

One minor suggestion, renaming the title and moving the initial sentence.

[julianocosta89]

LGTM, just waiting on open-telemetry/opentelemetry-helm-charts#1367