Delay the creation of the LogfileHandler

[LecrisUT]

Preparation for some refactoring of the workdir initialization logic, see the comment

tmt/tmt/utils/__init__.py

Lines 2463 to 2470 in eb8ed04

	# TODO: chicken and egg problem: when `Common` is instantiated, the workdir
	# path might be already known, but it's often not created yet. Therefore
	# a logfile handler cannot be attached to the given logger.
	# This is a problem, as we modify a given logger, and we may modify the
	# incorrect logger, and we may modify 3rd party app logger. The solution
	# to our little logging problem would probably be related to refactoring
	# of workdir creation some day in the future.
	self._logger.add_logfile_handler(workdir / tmt.log.LOG_FILENAME)

The purpose of this is to be able to:

• move the logic of defining the Common._workdir is defined and make it available much earlier. Refactoring where/when to do the creation of the workdir would follow afterwards
• move where the add_logfile_handler is executed and do not add it unless we are in a tmt run loop

---

Pull Request Checklist

• implement the feature

Depends-on: #4642

[gemini-code-assist]

Code Review

This pull request introduces a warnings.yaml log and refactors workdir loading. A change to LogfileHandler breaks stacktrace logging to files. The default for the new with_stacktrace parameter should be True to fix this for existing code. The handler for warnings.yaml must then explicitly set this to False.