allow unrecognized outputs and cell types in notebooks from the future

in nbformat schema / validation
Handle unrecognized outputs and cells from the future
fix loading of language name from kernel_info

language is langinfo.name, not langinfo.language

fixes highlighting for IJulia kernels
move language name, version into language_info

in kernel_info_reply

adds adaptation of language info to msgspec adapter
add language_info to nbformat doc and spec
update kernel_info_reply test
validate codemirror_mode
First stab at ConfigManager class
Add default for profile_dir

So ConfigManager is useful outside an IPython application
Remove profile_dir from handler class
Always depend on gnureadline if setupext.check_for_readline() fails

The inconsistency (asymmetry) of unconditionally adding gnureadline as a
dependency of binary distributions can cause issues like reported at
https://github.com/paylogic/pip-accel/issues/34
Add docstring documentation for widget_float
Preserve nbformat_minor from the future

warn on click of unrecognized elements, rather than on load.
close pager on escape on command mode
Added changes to dosctring documentation in widget_float.py (previous docstring written by me).
Added docstring documentation in widget_bool.py.
Pin the version of less used in the Dockerfile.
Update package name in error prompt.
Merge pull request #6991 from minrk/unhandled-types

Handle unrecognized output and cell types
Merge pull request #7070 from rgbkrk/pin_less_docker

Pin the version of less used in the Dockerfile
Don't calculate default value when setting traitlet for the first time