Help users with migration to the new compiler/SDK release

### Why

We have users now and we need to take care and guide them through the process of migrating their projects to the new compiler and SDK versions.

### What

1. Rust toolchain version changes (update `rust-toolchain.toml`). Occasionally, it requires adding/changing some attributes in the user's code (latest - `#![feature(alloc_error_handler)]`)
2. Breaking Miden SDK API changes.
3. Breaking changes in the SDK macros (`#[component]`, `#[note_script]`, etc.)

### How

#### 1. Instructions

I suggest we put the migration guides in our CHANGELOGs.

##### SDK
We have CHANGELOG.md in the `sdk` folder where we can put the migration guides for 2. and 3. I generate it manually every time I do an SDK release. I recommend we switch to requiring changes to it (on CI) in every PR that touches SDK (similar to the VM repo).

##### Compiler
We have CHANGELOG.md in the root folder where we can put the migration guides for 1. It's autogenerated by the `releaze-plz` and it is mostly garbage. So it's time to start writing it manually as well requiring every commit to update it or explicitly opt-out.

#### 2. Automation

cargo-miden should check the rustc nightly version in the user's `rust-toolchain.toml` and update it if needed. Besides that, it could also check for missing `#![feature(alloc_error_handler)]`, etc.