plugin(basic-auth): update the schema

[liuxiran]

Please answer these questions before submitting your issue.

• Why do you submit this issue?
• Question or discussion
• Bug
• Requirements
• Feature or performance improvement
• Other

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Question

• What do you want to know?

What is the purpose of SELECT item？

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Bug

• Which version of Apache APISIX Dashboard, OS, and Browser?

• What happened?
  If possible, provide a way to reproduce the error.

1. config basic-auth plugin for a route

2. select work with consumer object, and then click [ok]button

3. action failed , and got an validate error in the console
   

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Requirement or improvement

• Please describe your requirements or improvement suggestions.

[liuxiran]

Part of #2082

Accoring to the basic-auth doc :
config basic-auth plugin only needs to config
username(required) and password(required)

current schema of basic-auth:(update apisix to latest master branch)

{
	"additionalProperties": false,
	"properties": {
		"disable": {
			"type": "boolean"
		}
	},
	"title": "work with route or service object",
	"type": "object"
}

with the plugin page looks:

---

the expected schema should be:

{
  "type": "object",
  "required": [
    "username",
    "password"
  ],
  "properties": {
    "username": {
      "type": "string",
      "title": "Username"
    },
    "password": {
      "type": "string",
      "title": "Password"
    }
  }
}

with the plugin page looks:

[liuxiran]

The solution is the same with #2441, it has already worked well with the apisix master branch and dashboard v2.0 branch.

close is now :)