feat : AlertManager Role, allow using web config file

[modship]

This PR allow using web config file, in my case i need to use basic auth

Exemple :

alertmanager_web_config:
  basic_auth_users:
    John: $2a$12$9kqglntQUzvOFu2cvEYZ0.H6sXuho5Xdc.ID.C2hNtlCYF6q/RXWG
    Doe: $2a$12$sIB6/w8/4Fn5EWaAdrpSGuRqIhkrXzSnQSxOqbiSPhTbdHWkC.oKG

[SuperQ]

This does not follow the implementation pattern of the other roles.

This needs a DCO sign-off. You can use git commit -s --amend to add it.

[SuperQ]

This needs to use ansible.builtin.template like the other roles do.

[gardar]

@modship can you please rebase so that we can get this merged?