Add a new command doctor to check if some wrong configurations on gitea instance (#9095)

* add doctor

* Add a new command doctor to check if some wrong configurations on gitea instance

* fix import

* use regex match authorized_keys on doctor

* Add documentation

doc/usage/command-line.en-us.md

@@ -289,3 +289,28 @@ This command is idempotent.
 
 #### convert
 Converts an existing MySQL database from utf8 to utf8mb4.
+
+#### doctor
+Diagnose the problems of current gitea instance according the given configuration.
+Currently there are a check list below:
+
+- Check if OpenSSH authorized_keys file id correct
+When your gitea instance support OpenSSH, your gitea instance binary path will be written to `authorized_keys` 
+when there is any public key added or changed on your gitea instance.
+Sometimes if you moved or renamed your gitea binary when upgrade and you haven't run `Update the '.ssh/authorized_keys' file with Gitea SSH keys. (Not needed for the built-in SSH server.)` on your Admin Panel. Then all pull/push via SSH will not be work.
+This check will help you to check if it works well.
+
+For contributors, if you want to add more checks, you can wrie ad new function like `func(ctx *cli.Context) ([]string, error)` and 
+append it to `doctor.go`.
+
+```go
+var checklist = []check{
+	{
+		title: "Check if OpenSSH authorized_keys file id correct",
+		f:     runDoctorLocationMoved,
+    },
+    // more checks please append here
+}
+```
+
+This function will receive a command line context and return a list of details about the problems or error.