Exposing TimeEstimate field in the API (#35475)

Time Estimate field is not included in the issue modification webhooks
or issue API endpoints.

This PR fixes the field for the API.

---------

Signed-off-by: Gnanakeethan Balasubramaniam <gnanakeethan@users.noreply.github.com>
Signed-off-by: Gnanakeethan Balasubramaniam <gnanakeethan@cloudparallax.com>

modules/structs/issue.go

@@ -76,6 +76,8 @@ type Issue struct {
 	// swagger:strfmt date-time
 	Deadline *time.Time `json:"due_date"`
 
+	TimeEstimate int64 `json:"time_estimate"`
+
 	PullRequest *PullRequestMeta `json:"pull_request"`
 	Repo        *RepositoryMeta  `json:"repository"`