Convert bool string comparisons to strconv.ParseBool for REST parameters (#13650)

* Convert bool string comparisons to strconv.ParseBool for REST parameters

* Log failed bool conversions

* Rename errors, changed log levels

* drop strconv.ParseBool error handling

If the query string parameter is omitted, strconv.ParseBool returns an error for the empty strings, which spams the logs. Instead, just assume the default semantics of a `false` return value if an error occurs.

* allow randomized Client4 booleans

It's hard to test api4's handling of the various boolean input values
accepted. Extend Client4 with support for overriding how it builds those
strings, and pick a random value on test startup.

* gofmt -s

Co-authored-by: mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>
Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

api4/file.go

@@ -464,10 +464,7 @@ func getFile(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	forceDownload, convErr := strconv.ParseBool(r.URL.Query().Get("download"))
-	if convErr != nil {
-		forceDownload = false
-	}
+	forceDownload, _ := strconv.ParseBool(r.URL.Query().Get("download"))
 
 	auditRec := c.MakeAuditRecord("getFile", audit.Fail)
 	defer c.LogAuditRec(auditRec)
@@ -508,11 +505,7 @@ func getFileThumbnail(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	forceDownload, convErr := strconv.ParseBool(r.URL.Query().Get("download"))
-	if convErr != nil {
-		forceDownload = false
-	}
-
+	forceDownload, _ := strconv.ParseBool(r.URL.Query().Get("download"))
 	info, err := c.App.GetFileInfo(c.Params.FileId)
 	if err != nil {
 		c.Err = err
@@ -591,11 +584,7 @@ func getFilePreview(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	forceDownload, convErr := strconv.ParseBool(r.URL.Query().Get("download"))
-	if convErr != nil {
-		forceDownload = false
-	}
-
+	forceDownload, _ := strconv.ParseBool(r.URL.Query().Get("download"))
 	info, err := c.App.GetFileInfo(c.Params.FileId)
 	if err != nil {
 		c.Err = err