Build modified streamline images

The official image from streamline does not currently work for the arm64
platform. As a temporary measure, the source code and docker build scripts
have been lifted from the official images and are used to build locally.

Some additional modifications are made to reduce overall image size, these
are documented in docker/README.md

docker/streamline-src/vendor/sebastian/version/README.md

@@ -0,0 +1,50 @@
+[![Latest Stable Version](https://poser.pugx.org/sebastian/version/v/stable.png)](https://packagist.org/packages/sebastian/version)
+
+# sebastian/version
+
+**sebastian/version** is a library that helps with managing the version number of Git-hosted PHP projects.
+
+## Installation
+
+You can add this library as a local, per-project dependency to your project using [Composer](https://getcomposer.org/):
+
+```
+composer require sebastian/version
+```
+
+If you only need this library during development, for instance to run your project's test suite, then you should add it as a development-time dependency:
+
+```
+composer require --dev sebastian/version
+```
+## Usage
+
+The constructor of the `SebastianBergmann\Version` class expects two parameters:
+
+* `$release` is the version number of the latest release (`X.Y.Z`, for instance) or the name of the release series (`X.Y`) when no release has been made from that branch / for that release series yet.
+* `$path` is the path to the directory (or a subdirectory thereof) where the sourcecode of the project can be found. Simply passing `__DIR__` here usually suffices.
+
+Apart from the constructor, the `SebastianBergmann\Version` class has a single public method: `asString()`.
+
+Here is a contrived example that shows the basic usage:
+
+```php
+<?php declare(strict_types=1);
+use SebastianBergmann\Version;
+
+$version = new Version('1.0.0', __DIR__);
+
+var_dump($version->asString());
+```
+```
+string(18) "1.0.0-17-g00f3408"
+```
+
+When a new release is prepared, the string that is passed to the constructor as the first argument needs to be updated.
+
+### How SebastianBergmann\Version::asString() works
+
+* If `$path` is not (part of) a Git repository and `$release` is in `X.Y.Z` format then `$release` is returned as-is.
+* If `$path` is not (part of) a Git repository and `$release` is in `X.Y` format then `$release` is returned suffixed with `-dev`.
+* If `$path` is (part of) a Git repository and `$release` is in `X.Y.Z` format then the output of `git describe --tags` is returned as-is.
+* If `$path` is (part of) a Git repository and `$release` is in `X.Y` format then a string is returned that begins with `X.Y` and ends with information from `git describe --tags`.