Add app.in_foreground to search list (#6419)

Author: marandaneto

src/docs/product/sentry-basics/search/searchable-properties.mdx

@@ -81,6 +81,7 @@ Release properties overlap with event and issue search properties, so they don't
 | activity | Replay activity is calculated based on the number of errors, the number of ui events, and the duration of the replay. It's represented as a number from `1` to `10`. | | | x | number |
 | age | Returns issues created since the time defined by the value. The syntax is similar to the Unix find command. Supported suffixes: `m - minutes`, `h - hours`, `d - days`, `w - weeks`. For example, `age:-24h` returns isssues that are new in the last 24 hours, while `age:+12h` returns ones that are older than 12 hours. Entering `age:+12h age:-24h` would return issues created between 12 and 24 hours ago. |  | x |  | relative time |
 | apdex(threshold) | Returns results with the [Apdex score](/product/performance/metrics/#apdex) that you entered. Values must be between `0` and `1`. Higher apdex values indicate higher user satisfaction. | x |  |  | number |
+| app.in_foreground | Indicates if the app is in the foreground or background. | x | x |  | boolean |
 | assigned | Returns issues assigned to the defined user. Values can be a user ID (your email address), `me` for yourself, `me_or_none` for yourself or no assignee, or # followed by the team name, that is `#team-name`. |  | x |  | team or org user |
 | assigned_<br></br>or_suggested | Returns issues assigned to or suggested to be assigned to the defined user. Suggested assignees are determined by matching [ownership rules](/product/error-monitoring/issue-owners/) and [suspect commits](/product/issues/suspect-commits/). Values can be a user ID (your email address), `me` for yourself, `me_or_none` for yourself or no assignee/suggestions, or # followed by the team name, that is `#team-name`. |  | x |  | team or org user |
 | avg(field) | Returns results with matching averages for the field selected. The field can be either a number or a duration. Typically used with a comparison operator. | x |  |  | matches field |