Prior to this commit there were some layout issues in KanbanView:
1. The `o_kanban_header` z-index was not high enough and some icons in
the record element could hide it partially.
2. The `o_ghost_avatar` was not visible (white on white).
3. `.container` elements placed inside a record had their width
constrained by the grid system. This commit "fix the issue" setting
their max-width to 'none'.
Note on point 3:
To have '.container' max-width limited by the current resolution is not
a bug but the default grid-system behavior. This commit provides a
temporary workaround since 'container-fluid' classes should have been
used instead.
task-2892062
Part-of: odoo/odoo#96195
Brieuc-brd
ee46a9fda9