Bump rxjs from 6.6.7 to 7.5.5 in /src-ui

Bumps [rxjs](https://github.com/reactivex/rxjs) from 6.6.7 to 7.5.5.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/reactivex/rxjs/compare/6.6.7...7.5.5)

---
updated-dependencies:
- dependency-name: rxjs
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

src-ui/package.json

@@ -31,7 +31,7 @@
     "ngx-cookie-service": "^13.1.2",
     "ngx-file-drop": "^13.0.0",
     "ngx-infinite-scroll": "^10.0.1",
-    "rxjs": "~6.6.7",
+    "rxjs": "~7.5.5",
     "tslib": "^2.3.1",
     "uuid": "^8.3.1",
     "zone.js": "~0.11.4"