Fix bigip_user module's doc. Adding log-manager role to partition_acc…

[mahoutukaisali]

Summary:
This PR updates the documentation for the f5networks.f5_modules.bigip_user module to include a missing valid choice.

The Problem:
The DOCUMENTATION string for the bigip_user module's partition_access parameter does not list log-manager as a valid choice for the role sub-option.

Here is the F5 BIG-IP v17.x documentation for the user's roles: https://techdocs.f5.com/en-us/bigip-17-0-0/big-ip-systems-user-account-administration/user-roles.html

The Fix:
According to our testing on BIG-IP v17.x (and confirmed by the user in this playbook), the log-manager role is indeed accepted by the API when set as a partition role.

Example Playbook:

  tasks:
    - name: Update the user 'johnd' as an Log Manager
      f5networks.f5_modules.bigip_user:
        username_credential: johnd
        password_credential: password
        full_name: John Doe
        partition_access:
          - all:log-manager
        update_password: on_create
        provider:
          server: lb.mydomain.com
          user: admin
          password: secret
        state: present
      delegate_to: localhost

This PR adds log-manager to the choices list, so that the generated documentation on docs.ansible.com reflects the module's actual capabilities.