added design doc for sparse checkout

research/design-doc/sparse_checkout_asishkumar.md

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+# KPM sparse checkout
+
+**Author**: Asish Kumar
+
+## Solution
+
+In order to add the feature of sparse-checkout, kpm will add the package specified in the kcl.mod file and later when running `kcl mod run` it will checkout that destination directory which contains that package recursively. 
+
+## User Interface
+
+In order to use a specified package within a repository, the user will have to specify the package during the `kcl mod add` command. For example
+
+```
+kcl mod add --git https://github.com/officialasishkumar/check-kcl.git --commit 831fada36e155c8758f07f293c8267c869af69d3 --package k8s
+```
+
+This command will recursively search for the package name within all the existing kcl.mod files in the repository and load it by specifying the package name in `kcl.mod` under `dependencies`.
+
+The package flag is optional. If not provided kpm will work normally as before and you will need to have a `kcl.mod` file in the root of the repository. 
+
+There is also an option to manually write the package flag in `kcl.mod` file. For example: 
+
+```
+[dependencies]
+agent = { git = "https://github.com/kcl-lang/modules.git", commit = "ee03122b5f45b09eb48694422fc99a0772f6bba8", package = "agent" }
+```
+
+This will work the same way as before only thing to note is you need to have a `kcl.mod` file in the root of the repository when running the command: 
+
+```
+kcl mod add --git <url> --commit <hash>
+```
+
+The user can then run `kcl mod run` to run the code: 
+
+`kcl mod run`
+
+This will checkout the destination directory which contains that package within the repository. You can then use the loaded dependencies in your code.
+
+The user can also run the following commands with package in there `kcl.mod` file: 
+
+```
+kcl mod metadata
+```
+
+```
+kcl mod metadata --update
+```
+
+```
+kcl mod metadata --vendor
+```
+
+```
+kcl mod graph
+```
+
+## Design
+
+In order to use this feature, a new field `package` will be added to the `kcl.mod` file. This field will contain the package name that the user wants to use. 
+
+Earlier the download only happens, in case of git, when there is a `kcl.mod` file in the root. Enabling this feature, will allow download of git repository even when there is no `kcl.mod` file in the root but this will only work if a package flag is passed. 
+
+
+# Implementation and conclusion
+
+The idea implemented in the following PR was mentioned in https://github.com/kcl-lang/kpm/pull/335#issuecomment-2151338180.  
+
+Here are the merged PRs: 
+
+- https://github.com/kcl-lang/kpm/pull/453
+- https://github.com/kcl-lang/kpm/pull/457
+
+The changes made are tested by unit tests.