feat: support for embedding code snippets

[mdelapenya]

Description

This pull request includes changes to the Dockerfile, documentation, and template files to support embedding code snippets from the testcontainers-go repository into the documentation. The most important changes include adding a new build stage to clone the testcontainers-go repository, updating the documentation to include an embedded code snippet, and modifying the shortcode template to handle these embedded snippets.

Dockerfile changes:

• Added a new build stage git-src-oss to clone the testcontainers-go repository and copy it to the project directory ([DockerfileR36-R45](https://github.com/docker/docs/pull/22226/files#diff-dd2c0eb6ea5cfc6c4bd4eac30934e2d5746747af48fef6da689e85b752f39557R36-R45)).

Documentation changes:

• Updated content/manuals/testcontainers.md to include an embedded Go code snippet from the testcontainers-go repository ([content/manuals/testcontainers.mdR45-R46](https://github.com/docker/docs/pull/22226/files#diff-7905b168f0bee5db6711b541f42c48f5d0901c8cdc17f323e3c1725a5445a3dcR45-R46)).

IMPORTANT: this change is a demonstration on how to use the embedding shortcode.

Template changes:

• Created layouts/shortcodes/embedded.html to handle embedded code snippets, including logic to identify and extract specific code sections based on custom tags ([layouts/shortcodes/embedded.htmlR1-R65](https://github.com/docker/docs/pull/22226/files#diff-dc256c151d3b9c325236dc0c38d0ef5155ce617bb93d44b669b7641a00fbe42aR1-R65)).

The tag is using the following format:

• start tag: // START $id
• end tag: // END $id

Exception: for testcontainers-go, where this mechanism already exists, we are using different start/end tags:

• start tag: // $id {
• end tag: // }

Reviews

• Technical review
• Editorial review
• Product review

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[mdelapenya]

Before merging this PR, this line is just an example on how to use it, so it should be removed from here.

[crazy-max]

I think we should use vendoring through go mod convention of hugo if we need to use external resources like we do for cli reference docs:

• https://github.com/docker/docs/blob/main/go.mod
• https://github.com/docker/docs/tree/main/_vendor

Also git clone without pinning to commit sha is not reproducible and can lead to regressions with unrelated changes.

[mdelapenya]

Indeed, this is a PoC, and during the initial discussion with the Docs team we considered having the code snippets living in the docs repo, so the upstream repo (i.e. tc-go) would have to send a PR to the docs syncing the code snippets. As a result, no git clone would be needed, and the embedded short-code would just read from a local path, ideally next to the docs page using the code.