add ADR about caching

docs/adrs/0000-caching-dependencies.md

@@ -0,0 +1,43 @@
+# 0. Caching dependencies
+Date: 2022-03-29
+
+Status: Accepted
+
+# Context
+`actions/setup-go` is the one of the most popular action related to Golang in GitHub Actions. A lot of customers use it in conjunction with [actions/cache](https://github.com/actions/cache) to speed up dependencies installation.  
+See more examples on proper usage in [actions/cache documentation](https://github.com/actions/cache/blob/main/examples.md#go---modules).
+
+# Goals & Anti-Goals
+Integration of caching functionality into `actions/setup-go` action will bring the following benefits for action users:
+- Decrease the entry threshold for using the cache for Go dependencies and simplify initial configuration
+- Simplify YAML pipelines because no need additional steps to enable caching
+- More users will use cache for Go so more customers will have fast builds!
+
+We don't pursue the goal to provide wide customization of caching in scope of `actions/setup-go` action. The purpose of this integration is covering ~90% of basic use-cases. If user needs flexible customization, we should advice them to use `actions/cache` directly.
+
+# Decision
+- Add `cache` input parameter to `actions/setup-go`. For now, input will accept the following values: 
+  - `true` - enable caching for go dependencies
+  - `false` and `''` - disable caching for go dependencies. It will be set by default
+We're planing to get this values as strings, because if we'll get proposla for possible future tool, it will be easier to adjust logic
+- Cache feature will be disabled by default to make sure that we don't break existing customers. We will consider enabling cache by default in next major releases
+- Action will try to search a go.sum files in the repository and throw error if no one is found
+- The hash of found file will be used as cache key (the same approach like [actions/cache](https://github.com/actions/cache/blob/main/examples.md#go---modules) recommends)
+- The following key cache will be used `${{ runner.os }}-go${{ go-version }}-${{ hashFiles('<package-lock-path>') }}`
+- Action will cache global cache from the `go env GOCACHE` command
+
+# Example of real use-cases
+
+```yml
+steps:
+- uses: actions/checkout@v3
+- uses: actions/setup-go@v3
+  with:
+    go-version: '14'
+    cache: true
+```
+
+# Release process
+
+As soon as functionality is implemented, we will release minor update of action. No need to bump major version since there are no breaking changes for existing users.
+After that, we will update [starter-workflows](https://github.com/actions/starter-workflows/blob/main/ci/go.yml)