Add GitHub Action with automatic tag creation on push to main

[mpfmorawski]

Hello @FrancescoSaverioZuppichini! 👋

I noticed in README.md that GitHub Action described as "auto creating a new tag on push on main, sync versions" is still on the to do list. Due to the fact that I've been playing with GitHub Actions lately, I decided to implement it.
I hope I understood correctly your idea of this workflow.

PR Description

This PR introduces a new GitHub Actions workflow, create_tag.yml, to automate the creation of tags whenever the version in pyproject.toml changes. Here's a quick breakdown of the workflow logic:

GitHub Action trigger

It runs on every push to the main branch (specifically when pyproject.toml was modified).

GitHub Action key steps

1. Extract version from pyproject.toml
2. Check if the tag with this version already exists
3. Create and push the tag (if it doesn't exist)

How has it been tested?

I tested it on the fork of this repository:

• GitHub Action when tag was created -> Release v0.1.3 tag
• GitHub Action when tag was not created because tag related to this version already exists