Release evidence documentation

What does this MR do?

Documentation for #38103 (closed)

Related issues

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• [-] If applicable, update the permissions table.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.

/label documentation

doc/user/project/releases/index.md

@@ -107,6 +107,16 @@ For private projects, the number of Releases is displayed to users with Reporter
 [permissions](../../permissions.md#releases-permissions) or higher. For public projects,
 it is displayed to every user regardless of their permission level.
 
+### Upcoming Releases
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/issues/38105) in GitLab 12.1.
+
+A Release may be created ahead of time by specifying a future `released_at` date. Until
+the `released_at` date and time is reached, an **Upcoming Release** badge will appear next to the
+Release tag. Once the `released_at` date and time has passed, the badge is automatically removed.
+
+![An upcoming release](img/upcoming_release_v12_7.png)
+
 ## Editing a release
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/26016) in GitLab 12.6.
@@ -245,6 +255,19 @@ Please note that Release Evidence's data is collected regardless of this
 feature flag, which only enables or disables the display of the data on the
 Releases page.
 
+### Scheduled Evidence creation
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/23697) in GitLab 12.8.
+
+When the `released_at` date and time is not provided, the date and time of Release
+creation is used. The Evidence collection background job is immediately executed.
+
+If a future `released_at` is specified, the Release becomes an **Upcoming Release**. In this
+case, the Evidence is scheduled to be collected at the `released_at` date and time, via a
+background job.
+
+If a past `released_at` is used, no Evidence is collected for the Release.
+
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues