[MM-51201/MM-60406/MM-60404] CrossTeam Search posts and files (#28478)

* poc - wip

* add search files across teams

* eslint

* fix existing tests

* fix webapp style

* fix test

* add api doc

* change initial state in test

* add tests on API

* add tests on file info layer

* fix file search tags

* add rhs reducer test

* reset team selected when the RHS is suppressed

* change css to reflect UI

* fix style

* fix doc wording

* make getSearchTeam return currentTeamId when value is not set

* await is unnecessary

* revert boolean check and add test

* add comment to getSearchTeam to let dev knows it defaults to currentTeam

* remove redundant team check

* simplfy test

* fix style check

---------

Co-authored-by: Caleb Roseland <caleb@calebroseland.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/client4.go

@@ -4415,7 +4415,12 @@ func (c *Client4) SearchFilesWithParams(ctx context.Context, teamId string, para
 	if err != nil {
 		return nil, nil, NewAppError("SearchFilesWithParams", "api.marshal_error", nil, "", http.StatusInternalServerError).Wrap(err)
 	}
-	r, err := c.DoAPIPost(ctx, c.teamRoute(teamId)+"/files/search", string(js))
+
+	route := c.teamRoute(teamId) + "/files/search"
+	if teamId == "" {
+		route = c.filesRoute() + "/search"
+	}
+	r, err := c.DoAPIPost(ctx, route, string(js))
 	if err != nil {
 		return nil, BuildResponse(r), err
 	}
@@ -4428,6 +4433,15 @@ func (c *Client4) SearchFilesWithParams(ctx context.Context, teamId string, para
 	return &list, BuildResponse(r), nil
 }
 
+// SearchFilesAcrossTeams returns any posts with matching terms string.
+func (c *Client4) SearchFilesAcrossTeams(ctx context.Context, terms string, isOrSearch bool) (*FileInfoList, *Response, error) {
+	params := SearchParameter{
+		Terms:      &terms,
+		IsOrSearch: &isOrSearch,
+	}
+	return c.SearchFilesWithParams(ctx, "", &params)
+}
+
 // SearchPosts returns any posts with matching terms string.
 func (c *Client4) SearchPosts(ctx context.Context, teamId string, terms string, isOrSearch bool) (*PostList, *Response, error) {
 	params := SearchParameter{

server/public/model/feature_flags.go

@@ -55,6 +55,8 @@ type FeatureFlags struct {
 	NotificationMonitoring bool
 
 	ExperimentalAuditSettingsSystemConsoleUI bool
+
+	ExperimentalCrossTeamSearch bool
 }
 
 func (f *FeatureFlags) SetDefaults() {
@@ -78,6 +80,7 @@ func (f *FeatureFlags) SetDefaults() {
 	f.WebSocketEventScope = true
 	f.NotificationMonitoring = true
 	f.ExperimentalAuditSettingsSystemConsoleUI = false
+	f.ExperimentalCrossTeamSearch = false
 }
 
 // ToMap returns the feature flags as a map[string]string