Allow access to project metadata during context formatting.

[ianjosephwilson]

This is what I have right now using backticks which is repetitive and inefficient (minor in this case).

[tool.hatch.envs.default.scripts]
tag=[
    "git tag -a v`hatch version` -m 'Version `hatch version`'",
    "git push origin v`hatch version`"
]

This would be more concise and doesn't execute hatch 3 additional times:

[tool.hatch.envs.default.scripts]
tag=[
    "git tag -a v{project.version} -m 'Version {project.version}'",
    "git push origin v{project.version}"
]