add attribute for tracking preview usage in the codebase (#2128)

Octokit/Clients/ProjectColumnsClient.cs

@@ -38,6 +38,7 @@ namespace Octokit
         /// </remarks>
         /// <param name="projectId">The Id of the project</param>
         /// <param name="options">Options for changing the API response</param>
+        [Preview("inertia")]
         [ManualRoute("GET", "projects/{project_id}/columns")]
         public Task<IReadOnlyList<ProjectColumn>> GetAll(int projectId, ApiOptions options)
         {
@@ -53,6 +54,7 @@ namespace Octokit
         /// See the <a href="https://developer.github.com/v3/projects/columns/#get-a-project-column">API documentation</a> for more information.
         /// </remarks>
         /// <param name="id">The id of the column</param>
+        [Preview("inertia")]
         [ManualRoute("GET", "projects/columns/{column_id}")]
         public Task<ProjectColumn> Get(int id)
         {
@@ -67,6 +69,7 @@ namespace Octokit
         /// </remarks>
         /// <param name="projectId">The Id of the project</param>
         /// <param name="newProjectColumn">The column to create</param>
+        [Preview("inertia")]
         [ManualRoute("POST", "projects/{project_id}/columns")]
         public Task<ProjectColumn> Create(int projectId, NewProjectColumn newProjectColumn)
         {
@@ -83,6 +86,7 @@ namespace Octokit
         /// </remarks>
         /// <param name="id">The id of the column</param>
         /// <param name="projectColumnUpdate">New values to update the column with</param>
+        [Preview("inertia")]
         [ManualRoute("PATCH", "projects/columns/{column_id}")]
         public Task<ProjectColumn> Update(int id, ProjectColumnUpdate projectColumnUpdate)
         {
@@ -98,6 +102,7 @@ namespace Octokit
         /// See the <a href="https://developer.github.com/v3/projects/columns/#delete-a-project-column">API documentation</a> for more information.
         /// </remarks>
         /// <param name="id">The id of the column</param>
+        [Preview("inertia")]
         [ManualRoute("DELETE", "projects/columns/{column_id}")]
         public async Task<bool> Delete(int id)
         {
@@ -121,6 +126,7 @@ namespace Octokit
         /// </remarks>
         /// <param name="id">The id of the column</param>
         /// <param name="position">The position to move the column</param>
+        [Preview("inertia")]
         [ManualRoute("POST", "projects/columns/{column_id}/moves")]
         public async Task<bool> Move(int id, ProjectColumnMove position)
         {