Detect inconsistent versions between default toolchain and Forc manifest version

[eightfilms]

fuelup should be able to do both these things:

• Set the default toolchain version.
• Enable reading of the default toolchain version (so that forc can detect when you're using the wrong version that doesn't match what's configured in the manifest file).

As mentioned here, this would probably require some design decisions on what constitutes a stable toolchain and how we reconcile forc and fuel-core compatibility

Update:

With FuelLabs/sway#2405 now merged, we can detect inconsistent versions by matching with the minimum forc-version specified in the Forc.toml.

[eightfilms]

Since part 1 is already done with the introduction of the fuelup default command, I'm going to rename this issue and leave the 2nd one up as a task.

[sdankel]

This is done using forc-toolchain.toml (overrides)