feat: Added support for execution of executable files within the scripts directories

[renatav]

Description (e.g. "Related to ...", etc.)

Added support for execution of executable files within the scripts directories

This was implemented and tested by @jc12690, but we couldn't merge the PR due to the commit history being severely out of sync with master. I'm fine with merging this in without in-depth testing, since we will need to do more work on the handlers soon and they are not being used atm

Closes #482

Code review checklist (for code reviewer to complete)

• [ ] Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• [ ] Title summarizes what is changing
• [ ] Commit messages are meaningful (see this for details)
• [ ] Tests have been included and/or updated, as appropriate
• [ ] Docstrings have been included and/or updated, as appropriate
• [ ] Changelog has been updated, as needed (see CHANGELOG.md)

[n-dusan]

Tested it and it works - thanks for working on this with us @jc12690!!

Proof:

...
    repos_and_data[script_repo]["data"] = execute_scripts(
  File "/home/dnikolic/taf/taf/updater/lifecycle_handlers.py", line 206, in execute_scripts
    raise ScriptExecutionError(script_path, e.output)
taf.exceptions.ScriptExecutionError: An error happened during execution of script /home/dnikolic/narf/scripts/narf-nill/law/update/completed/hello_world_script:

: Hello world from executable_py_script.py

I've pushed a small fix following the changes to latest master.