Support partial [package] section in wasmer.toml

[ayys]

For unnamed packaged, we need to add support for certain fields, but not others. wasmer.toml should support two kinds of [package] sections:

A minimal named package section

[package]
name = "someone/something"
version = "1.1.1"

A minimal unnamed package section

[package]

Invalid package section

[package]
version = "0.1.1"

Valid package section

[package]
name = "someone/something" # this could be supported as publishing a hash to this package

[xdoardo]

Closing, resolved by #4630.