docs: Update user-mgr to current implementation

Update architecture/user-management.md to reflect the current state
of phosphor-user-manager and PAM configuration.

Changes:
- Remove 'web' group
Ref: https://gerrit.openbmc.org/c/openbmc/phosphor-user-manager/+/70969

- Update path, interface, methods, properties

- PAM configuration changes
Ref: https://gerrit.openbmc.org/c/openbmc/openbmc/+/41357

- Update LDAP authorization
Ref: https://gerrit.openbmc.org/c/openbmc/phosphor-user-manager/+/84828

- Remove implemented items from Recommended Implementation

Change-Id: I2eb7da6a85b62f4ee4b557caa550185a6fdd99f0
Signed-off-by: Vijaysankar Ravi <vijaysankarr@ami.com>