Etherlink/Tezt: by default, print all the kernel logs of the EVM nodes

What

This commit changes the behavior of the Tezt wrapper of the EVM node to keep all the logs produced by the kernel instead of filtering out the DEBUG logs.

Why

To ease debugging. Note that this changes nothing if the kernel is compiled with the default set of options.

How

Manually testing the MR

• compile the kernel with debug-level logs:

make -f etherlink.mk EVM_KERNEL_FEATURES=debug build

• run your favorite scenario:

dune exec etherlink/tezt/tests/main.exe -- alpha --verbose -m '<...>' &> log

• enjoy the kernel logs:

grep --text 'write_debug` log | sed 's/.* \([A-Z]\+\).*write_debug\] \(.*\)/\1 \2/'

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR