docs: cargo features (#3527)

* dialog

* fs

* geolocation

* haptic

* log

* single instance

* notification

* updater

* ##

* persisted scopes

* stronghold

* sql

* upload

* websocket

* http
(this one was too long that I generated through codex, didn't review yet)

* add change file

* no persisted-scope-js

* add `://`

* Merge branch 'v2' into document-cargo-features

* update system-proxy docs

* finish http docs

* notification doesn't need version bumps

* clean up docs

.changes/feature-flags-docs.md

@@ -0,0 +1,30 @@
+---
+"dialog": patch
+"dialog-js": patch
+"fs": patch
+"fs-js": patch
+"geolocation": patch
+"geolocation-js": patch
+"haptics": patch
+"haptics-js": patch
+"http": patch
+"http-js": patch
+"log": patch
+"log-js": patch
+"persisted-scope": patch
+"positioner": patch
+"positioner-js": patch
+"single-instance": patch
+"sql": patch
+"sql-js": patch
+"stronghold": patch
+"stronghold-js": patch
+"updater": patch
+"updater-js": patch
+"upload": patch
+"upload-js": patch
+"websocket": patch
+"websocket-js": patch
+---
+
+Documented Cargo feature flags in each plugin's crate-level documentation.