Clean up FeatureFlagService

[maciej-szlosarczyk]

This is a cleanup of feature flag service from unused code, unwanted dependencies and some minor UI/code standard fixes.

For now the UI looks like this, I plan to update it to use the same styles as frontend in a separate PR.

Changes

• Remove unused deps (mailer, live dashboard)
• Clean up compilation warnings
• Remove unused code
• Rename function to more Elixir-like Featureflagservice.FeatureFlags.list_feature_flags/0
• Remove phoenix branding from UI
• Add buttons and nicer links

[cartersocha]

ty for submitting @maciej-szlosarczyk. I'll check out the portal experience. @open-telemetry/demo-webstore-approvers anyone have familiarity with phoenix? From a quick review it looks like a clean up to me but I can't comment on the finer details. Adding @tsloughter to take a quick look too

[tsloughter]

Looks great, thanks!

[tsloughter]

For anyone else reading this, I believe there is still more that can be cleaned up, so pls send PRs if you see anything :). Main stuff I'm thinking of that can probably go is stuff out of FeatureflagserviceWeb related to liveview and maybe some of the Plug's used in the router. For example, fetch_session sounds like one we don't need.

[maciej-szlosarczyk]

@tsloughter I think both have to stay - LiveView is used to render .heex templates, and session plug is required to use flash messages (put_flash(conn, :info, "Feature flag created successfully.")).

[cartersocha]

One thing to note is we're rebranding the front end. So maybe hold off on making this too aligned or detailed with the existing front end

[tsloughter]

@maciej-szlosarczyk ah! Thanks, I would have broken that :)

[mic-max]

LGTM!