package.json: use semver for webpack dependency

As far as I can tell dspace-angular doesn't explicitly need any
particular version of webpack itself, but angular-cli specifies
a semver string of `^5.54.0` so we should do the same.

Also, our dependabot configuration currently considers minor and
patch versions for updates, so we should not be using an exact
version here anyway.

See: https://github.com/angular/angular-cli/blob/18.2.x/packages/ngtools/webpack/package.json

package-lock.json

@@ -155,7 +155,7 @@
         "sass-resources-loader": "^2.2.5",
         "ts-node": "^8.10.2",
         "typescript": "~5.4.5",
-        "webpack": "5.101.0",
+        "webpack": "^5.54.0",
         "webpack-cli": "^5.1.4",
         "webpack-dev-server": "^5.2.2"
       }