core: add new `init_script_path` option: `init_script_path` option can be used in `[DEFAULTS]` to run a script at the end of backend initialisation. A new `init_pre_script` method is used to wait for backend to reach this stage (designed to be used mostly by CLI frontend), then the usual `ready_get` method is finished once the script is finished.

syntax: glob
bridge_constructor/generated
.build
build
ctags_links/
dist/
.eggs/
env/
libervia_backend.egg-info/
MANIFEST
.mypy_cache/
*.orig
*.pyc
*.pyo
.pytest_cache
*.pyv
Session.vim
stubs/
*.swo
*.swp
tags
tests/e2e/report*
_trial_temp/
twistd.log
twistd.pid
twisted/plugins/dropin.cache
*.un~
.vim
.vscode