Problem

OrganizationProvider.addManagedMember is supposed to add a user to an
organization with MembershipType.MANAGED, but the user ends up UNMANAGED
instead whenever the UserModel passed in came from the standard cached
user provider (e.g. session.users().getUserById(...), as used by custom
AdminRealmResourceProviders and other real callers of addManagedMember).

Root cause

JpaOrganizationProvider.addMember() calls user.joinGroup(group, metadata).
UserModel has a default implementation for that overload:

default void joinGroup(GroupModel group, MembershipMetadata metadata) {
    joinGroup(group);
}

The infinispan cache UserAdapter only overrides the single-arg
joinGroup(GroupModel), not the metadata-aware overload. So when user is
a cache-wrapped UserAdapter, the call falls through to the default
above, silently drops the MANAGED metadata, and ends up at the JPA
layer's joinGroup(group) -> joinGroup(group, null), which defaults the
membership type to UNMANAGED.

Fix

Added the missing joinGroup(GroupModel, MembershipMetadata) override to
the infinispan UserAdapter, mirroring the existing joinGroup(GroupModel)
override exactly, so the metadata is passed through to the delegate
instead of being dropped.

Testing

Added OrganizationCacheTest#testAddManagedMemberWithCachedUser, which
fetches a user through the normal cached user provider, calls
addManagedMember, and asserts isManagedMember is true.

• Verified the new test fails on the unfixed code
  (expected: but was: ) and passes with the fix.
• Ran the broader organization/cache/member test suites
  (OrganizationCacheTest, OrganizationMemberTest,
  OrganizationMemberIdpLinkTest, OrganizationInternalGroupTest,
  OrganizationGroupMembershipTest) - 60 tests, all passing, no
  regressions.
• ./mvnw spotless:check passes on the changed modules.

Closes #43094