feature(function): add custom functions documentation for AWS Amplify-backend

[MarlonJD]

… Gen 2 @aws-amplify/amplify-backend/1602

Description of changes:

Add custom runtime documents, it's required for #1602

Related GitHub issue

#1543, #1486

Instructions

Which product(s) are affected by this PR (if applicable)?

• amplify-backend
• amplify-ui
• amplify-studio
• amplify-hosting
• amplify-libraries

Which platform(s) are affected by this PR (if applicable)?

• JS
• Swift
• Android
• Flutter
• React Native

Please add the product(s)/platform(s) affected to the PR title
amplify-backend

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[sobolk]

I left two comments around docker and go. But I suggest to wait until @josefaidt gets a chance to review this before making changes.

[sobolk]

Suggested change

	<Callout warning>
	**Note:** Custom runtimes are not supported in Amplify Functions directly. If you need docker support to use a custom runtime for example in Python, Docker is not supported in Amplify Hosting and Amplify backend auto build. You shouldn't use docker build in your function.There is an example of how to use python in a lambda function in the without Docker section below.
	</Callout>
	<Callout warning>
	**Note:** [Fullstack Git-based environments](https://docs.amplify.aws/react/how-amplify-works/concepts/#fullstack-git-based-environments) do not support Docker for functions bundling out of the box.
	</Callout>

[sobolk]

We should refrain from using alpha packages in docs.

We should:

• either convert this sample to use Code.from.. and plain Function (like in case of python).
• or just remove Go sample.

[MarlonJD]

Here is an example of how this can be implemented using Function:

import { defineFunction } from "@aws-amplify/backend";
import { DockerImage, Duration } from "aws-cdk-lib";
import { Code, Function, Runtime } from "aws-cdk-lib/aws-lambda";
import { execSync } from "child_process";
import * as path from "path";
import { fileURLToPath } from "url";

const functionDir = path.dirname(fileURLToPath(import.meta.url));

export const sendSmsGoFunctionHandler = defineFunction(
  (scope) =>
    new Function(scope, "SendSmsGo", {
      handler: "bootstrap",
      runtime: Runtime.PROVIDED_AL2023, // or any other python version
      timeout: Duration.seconds(3), //  default is 3 seconds
      code: Code.fromAsset(functionDir, {
        bundling: {
          image: DockerImage.fromRegistry("dummy"),
          local: {
            tryBundle(outputDir: string) {
              execSync(`rsync -rLv ${functionDir}/* ${path.join(outputDir)}`);
              execSync(
                `cd ${path.join(outputDir)} && GOARCH=amd64 GOOS=linux go build -tags lambda.norpc -o ${path.join(outputDir)}/bootstrap ${functionDir}/main.go`
              );
              return true;
            },
          },
        },
      }),
    }),
);

[rdsimp]

Shouldn't this be amplify/functions/say-hello/index.py instead of amplify/functions/say-hello/handler.ts?