Deprecate `filepath` in Releases and Release Links API
### Overview
This epic aims to track all changes required to deprecate `filepath` field in [Releases](https://docs.gitlab.com/ee/api/releases) and [Releases Links](https://docs.gitlab.com/ee/api/releases/links.html) APIs by %"17.0".
As this is a breaking change to the API, we plan to continue supporting `filepath` until it is fully removed in %"17.0", but until then, we will also provide an alias (i.e. `direct_asset_path`) starting in %"15.9" to allow customers, and ourselves (read below) enough time to migrate.
When we reach %"17.0" , `filepath` will be removed, and `direct_asset_path` will be used moving forward.
### Why not in %"16.0"?
Since we internally use `filepath` in both [`gitlab-cli`](https://gitlab.com/gitlab-org/cli) and [`release-cli`](https://gitlab.com/gitlab-org/release-cli), we would also need to update our codebases to use `direct_asset_path`. Additionally, we need to update the ~frontend as well to reflect that change.
As [outlined](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/82966#note_1235573473) by @vshushlin, we need to do the following steps to ensure a smooth deprecation/rename of the field:
- Add `direct_asset_path` as an alias for `filepath`.
- Update ~frontend to use the new field.
- Update [release-cli](https://gitlab.com/gitlab-org/release-cli) to use the new field.
- Update [gitlab-cli](https://gitlab.com/gitlab-org/cli) to use the new field.
- Remove `filepath` from both APIs.
Each of these require a separate issue, which will be part of this epic.
epic