[PM-4154] Add PM-4154-bulk-encryption-service feature flag

[quexten]

Type of change

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

Objective

Adds the PM-4154-bulk-encryption-service feature flag for bitwarden/clients#6465.

Code changes

• file.ext: Description of what was changed and why

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

[github-actions]

Checkmarx One – Scan Summary & Details – edc572c8-46ec-4516-9167-00c55d1cd810

No New Or Fixed Issues Found