[SG-434] Remove gravatar.com from CSP rules

[djsmith85]

Type of change

- [ ] Bug fix
- [X] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

With some recent work to update the 2fa.directory urls, here's another spot where the gravatar-url's need to be removed.

Code changes

• docker-unified/hbs/nginx-config.hbs: Removed https://www.gravatar.com from CSP
• util/Setup/Configuration.cs: Removed https://www.gravatar.com from Nginx CSP

Before you submit

• Please check for formatting errors (dotnet format --verify-no-changes) (required)
• If making database changes - make sure you also update Entity Framework queries and/or migrations
• Please add unit tests where it makes sense to do so (encouraged but not required)
• If this change requires a documentation update - notify the documentation team
• If this change has particular deployment requirements - notify the DevOps team