Add pyproject.toml and GitLab CI for project setup

Introduced a `pyproject.toml` file to define project metadata, dependencies, and Python version requirements. Added a `.gitlab-ci.yml` for automated builds and PyPI package uploads in the CI pipeline.

.gitlab-ci.yml

+image: python:latest
+
+run-default:
+  rules:
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+  script:
+    - pip install build twine
+    - python -m build
+    - TWINE_PASSWORD=${CI_JOB_TOKEN} TWINE_USERNAME=gitlab-ci-token python -m twine upload --repository-url ${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/pypi dist/*

pyproject.toml

+[project]
+name = "python-mkp"
+version = "0.6.0"
+description = "Pack and unpack Check_MK mkp file"
+readme = "README.md"
+authors = [
+  {name = "Thomas Reifenberger", email = "tom-mi@users.noreply.github.com"},
+]
+dependencies = [
+    "requests",
+    "lxml",
+    "zeep",
+    "pydantic[email]",
+    "pydantic-xml",
+]
+requires-python = ">= 3.10"