Containerd-Shim: Enabling reading annotations: make annotations public e.g., for containerd-shims

[wlkrm]

I am working on a containerd-shim for wasm, which uses annotations to for some container-specific configuration parameters for the runtime. For this, I need access to the annotations in my Sandbox implementation. For this I am using the cointainerd_shim_wasm.
Effectifly, I run the following containerd command:

	sudo ctr run --rm --annotation --annotation 'my_config_param=example_config_value' runtime=./runwasi-shim localhost/wams-app:latest test2

I would need access to the annotations in the Sandbox run_wasi main function like this:

/// Main entry point. Checks if there are annotations.

use containerd_shim_wasm::{
    sandbox::{
        Sandbox,
        context::{RuntimeContext, WasmBinaryType},
    },
    shim::{Cli, Shim, Version, version},
};

impl Sandbox for MySandbox {    
    async fn run_wasi(&self, ctx: &impl RuntimeContext) -> Result<i32> {
        // Implement your Wasm runtime logic here
        let Entrypoint {
            source,
            func,
            arg0,
            name,
        } = ctx.entrypoint();
        log::info!("func: {}, arg0: {:?}, name: {:?}", func, arg0, name);
        // Access the annotations and do something specific for them
        let annotations = ctx.annotations().clone();

These annotation are very specific to my usecase and are out of scope of usual oci run annotations.

To achieve that, I need access to the currently private annotations.
The PR provides an API call to access them.

EDIT: also fixes two typos in docs.