Support for status check pattern (#24633)

This PR is to allow users to specify status checks by patterns. Users
can enter patterns in the "Status Check Pattern" `textarea` to match
status checks and each line specifies a pattern. If "Status Check" is
enabled, patterns cannot be empty and user must enter at least one
pattern.
Users will no longer be able to choose status checks from the table. But
a __*`Matched`*__ mark will be added to the matched checks to help users
enter patterns.

Benefits:
- Even if no status checks have been completed, users can specify
necessary status checks in advance.
- More flexible. Users can specify a series of status checks by one
pattern.

Before:

![image](635738ad-580c-49cd-941d-c721e5b99be4)

After:

![image](16aa7b1b-abf1-4170-9bfa-ae6fc9803a82)

---------

Co-authored-by: silverwind <me@silverwind.io>

services/forms/repo_form.go

@@ -199,7 +199,7 @@ type ProtectBranchForm struct {
 	MergeWhitelistUsers           string
 	MergeWhitelistTeams           string
 	EnableStatusCheck             bool
-	StatusCheckContexts           []string
+	StatusCheckContexts           string
 	RequiredApprovals             int64
 	EnableApprovalsWhitelist      bool
 	ApprovalsWhitelistUsers       string