[demo] Replace references to feature flag service with flagd

[austinlparker]

docs updates for v1.9, ff service deprecation in favor of flagd.

[austinlparker]

This is waiting for open-telemetry/opentelemetry-demo#1388 to merge before it can be reviewed

[julianocosta89]

LGTM, just a minor comment.

[svrnm]

only a few minor things.

If you want to, you can add flagd to the cspell.yml and add OpenFeature to textlintrc to make sure it is written in that form

[svrnm]

/fix:all

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You triggered fix:all action run at https://github.com/open-telemetry/opentelemetry.io/actions/runs/8234836163

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fix:all run failed, please check https://github.com/open-telemetry/opentelemetry.io/actions/runs/8234836163 for details

[svrnm]

I forgot an https in my suggestion, fixed that.

@austinlparker I have a list of PRs I am going to merge right now, I will handle this one as well.

[svrnm]

/fix:all

[github-actions]

You triggered fix:all action run at https://github.com/open-telemetry/opentelemetry.io/actions/runs/8235024578