Documentation: dev-tools: add container.rst page

Documentation: dev-tools: add container.rst page

Add a dev-tools/container.rst documentation page for the
scripts/container tool.  This covers the basic usage with additional
information about environment variables and user IDs.  It also
includes a number of practical examples with a reference to the
experimental kernel.org toolchain images.

Update MAINTAINERS accordingly with a reference to the added file.

Signed-off-by: Guillaume Tucker <gtucker@gtucker.io>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Tested-by: Nicolas Schier <nsc@kernel.org>
Acked-by: Nicolas Schier <nsc@kernel.org>
Link: https://patch.msgid.link/af886533cc5cbdd6ef1d909793b79a1ad42c74ca.1769090419.git.gtucker@gtucker.io
Signed-off-by: Nathan Chancellor <nathan@kernel.org>