Bump @angular/core from 5.2.11 to 11.0.5

Apache's new dependabot created the following PRs for Knox:

  - Bump @angular/core from 5.2.11 to 11.0.5 in /gateway-admin-ui #588
  - Bump @angular/core from 5.2.11 to 11.0.5 in /knox-homepage-ui #591
  - Bump @angular/core from 5.2.11 to 11.0.5 in /knox-token-management-ui #592

However, these PRs cannot be merged directly because there is a huge gap between the Angular version that is being used now and the one the bot tries to upgrade to. This requires additional development and testing on its own.