Email alias for maintainers to include in pyproject.toml

I created the pygmt.team@gmail.com email address that's listed in [pyproject.toml](https://github.com/GenericMappingTools/pygmt/blob/main/pyproject.toml) a couple years ago with the idea that it could be shared amongst all maintainers. However, gmail addresses are actually not good for shared use. We should find a way to create an alias instead that could be forwarded to a variable number of maintainers.