Fix Realm DisplayName Bug with Email Content enhancement

[vilmosnagy]

Description

Bug Report

There is a small issue with how realm display names are handled in email templates when the displayName of the realm is an empty string. This results in an email with a missing <realm-name> placeholder.

Example email body:

Someone requested a login link to  
Click to log in.

Cause:

• The `realmName˛ attribute is initially set with proper checks for empty strings.
• However, Keycloak's FreeMarkerEmailTemplateProvider overrides this attribute without handling empty strings properly.

Enhancement Request

We'd like to enhance the email behavior so that if the OAuth client has a name, it is used in place of the realm's displayName.

Proposed Fix and Enhancement

Bug Fix:

• Rename the realmName attribute to avoid conflicts with Keycloak's default behavior, ensuring empty strings are handled correctly.

Enhancement Implementation:

• Modify the email logic to prefer the client's name (if available) over the realm's displayName or name.