Opinion: Specify workdir on component instead of component build

Hey,

with #406 support for specifying the workdir for component build ([component.build]) was introduced. I wonder if it would make more sense to move the workdir property to [[component]]...

Moving workdir to the component level would allow Spin to re-use it when specifying component source

With the current implementation I end up with having the value of workdir twice (when sticking to default cargo build instructions)

[[component]]
id = "create-order"
source = "create_order/target/wasm32-wasi/release/create_order.wasm"
[component.trigger]
route = "/..."
[component.build]
workdir = "create_order"
command = "cargo build --target wasm32-wasi --release"

Actually, I'm not sure if component.source should automatically pick up the workdir or not, but it cloud lead to something like this:

[[component]]
id = "create-order"
workdir = "create_order"
source = "target/wasm32-wasi/release/create_order.wasm"
[component.trigger]
route = "/..."
[component.build]
command = "cargo build --target wasm32-wasi --release"

So internally, component source could be computed by combining workdir and source resulting again in
create_order/target/wasm32-wasi/release/create_order.wasm

Review Spin's current component configuration and build/source handling before proposing a change. The issue asks whether workdir should move from component.build to component and whether it should affect source resolution; done requires a maintainer decision on that behavior and an agreed implementation scope.