feat: Add conditional login passkeys

[waynemorphic]

Code review on this feature is highly welcome.

Keycloak reference

[OOub]

I'm looking into this feature as well and when I try this I get this error

Caused by: freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> authenticators  [in template "login-passkeys-conditional-authenticate.ftl" at line 117, column 45]

Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
----

----
FTL stack trace ("~" means nesting-related):
	- Failed at: ${authenticators}  [in template "login-passkeys-conditional-authenticate.ftl" at line 117, column 43]
	~ Reached through: #nested "form"  [in template "template.ftl" in macro "registrationLayout" at line 45, column 5]
	~ Reached through: @layout.registrationLayout script="di...  [in template "login-passkeys-conditional-authenticate.ftl" at line 8, column 1]
----
	at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
	at freemarker.core.EvalUtil.coerceModelToTextualCommon(EvalUtil.java:481)
	at freemarker.core.EvalUtil.coerceModelToStringOrMarkup(EvalUtil.java:401)
	at freemarker.core.EvalUtil.coerceModelToStringOrMarkup(EvalUtil.java:370)
	at freemarker.core.DollarVariable.calculateInterpolatedStringOrMarkup(DollarVariable.java:104)
	at freemarker.core.DollarVariable.accept(DollarVariable.java:63)
	at freemarker.core.Environment.visit(Environment.java:335)
	at freemarker.core.Environment.visit(Environment.java:377)
	at freemarker.core.Environment.invokeNestedContent(Environment.java:621)
	at freemarker.core.BodyInstruction.accept(BodyInstruction.java:60)
	at freemarker.core.Environment.visit(Environment.java:371)
	at freemarker.core.Environment.visit(Environment.java:398)
	at freemarker.core.BlockAssignment.accept(BlockAssignment.java:55)
	at freemarker.core.Environment.visit(Environment.java:371)
	at freemarker.core.Environment.invokeMacroOrFunctionCommonPart(Environment.java:877)
	at freemarker.core.Environment.invokeMacro(Environment.java:813)
	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:84)
	at freemarker.core.Environment.visit(Environment.java:335)
	at freemarker.core.Environment.visit(Environment.java:341)
	at freemarker.core.Environment.process(Environment.java:314)
	at freemarker.template.Template.process(Template.java:383)
	at org.keycloak.theme.freemarker.DefaultFreeMarkerProvider.processTemplate(DefaultFreeMarkerProvider.java:49)
	... 21 more

[waynemorphic]

@OOub thank you for your input on this. Yes, that error is expected. You could delete that line since this will remove that error. Alternatively, how could that section of the script be improved?