added the docs directory with design report for kpm sparse checkout

docs/kpm_sparse_checkout.md

@@ -0,0 +1,75 @@
+## KPM Sparse-Checkout feature
+
+## 1. Introduction
+kpm which is the package management tool for KCL, does not support sparse-checkout, which means an issue arises when dealing with monorepos, which may contain many KCL packages. We need to get a solution to download specific packages instead of all in a monorepo.
+
+## 2. User Worklow
+- Adding a Subdirectory Dependency via Command Line
+- Specifying a Subdirectory in `kcl.mod`
+- Adding a Subdirectory Dependency via Configuration File 
+
+## 3. Command Line Inteface 
+We will try to keep the command line interface as simple and straightforward as possible for adding a Git repository subdirectory as a dependency. The below steps show how a user can use the feature:
+
+- Adding a Dependency :
+The following command will lead to the addition of a dependency:
+`kcl mod add <repository_url> <subdirectory_path>`
+
+This command will add the specified subdirectory as a dependency in the current KCL project.
+
+- Non-interactive Method :
+In addition to the command line interface, users can specify subdirectory dependencies directly in the `kcl.mod` file, which can be particularly useful for automated environments.
+
+## 4. Example Use-case
+Considering the nginx-ingres module, on typing the command 
+
+```
+kcl mod add https://github.com/kcl-lang/modules/tree/main/nginx-ingress /restrict-ingress-anotations
+``` 
+
+The following command will lead to the addition of restrict-ingress-anotations package to the current KCL project and will update the kcl.mod accordingly.
+
+Alternatively, for non-interactive environments, users can directly edit the `kcl.mod` file:
+```
+[package]
+name = "test"
+edition = "v0.9.0"
+version = "0.0.1"
+
+[dependencies]
+my_dependency = { git = "https://github.com/example/repo", subdirectory = "path/to/package" }
+
+```
+
+## 5. Specifying how kcl.mod will specify the added subdirectories
+To support the specification of a subdirectory for dependencies that are sourced from Git repositories, we need to extend the kcl.mod file structure. This involves adding an optional `subdirectory` field under each dependency. This can be manually edited or automatically updated by the kcl mod add command.
+
+A sample kcl mod for the same would look like this.
+
+```
+[package]
+name = "test"
+edition = "v0.9.0"
+version = "0.0.1"
+
+[dependencies]
+my_dependency = { git = "https://github.com/example/repo", subdirectory = "path/to/package" }
+```
+
+## 6. Integration and the use of go-getter to download the specific subdirectories
+
+The repoUrl field in the struct `CloneOptions` in kpm/pkg/git/git.go will be given the subdir url accordingly, which then downloads each selected subdirectory one by one. KCL currently uses go-getter to download using URL's with ease.
+
+We can also provide a fallback mechanism to download the entire repo if the subdirectory download fails repeatedly by something like - 
+
+```Go
+err := downloadSubdir(repoUrl, subdir)
+if err != nil {
+    log.Printf("Failed to download subdirectory, falling back to full repository: %v", err)
+    return downloadRepo(repoUrl)
+}
+
+```
+
+## 7. Conclusion
+By extending the kcl.mod file to include a subdirectory field for Git-based dependencies, users can now specify and manage dependencies that reside in specific subdirectories of a Git repository. This enhancement will enable kpm to download only the necessary parts of large repositories, significantly improving performance when dealing with monorepos. The user interface remains intuitive, and the implementation leverages Git's sparse-checkout feature to achieve the desired functionality even when used in automated CI/CD pipelines.