feat: support to generate json output for explain analyze in http api (#5567)

* impl

Signed-off-by: Ruihang Xia <waynestxia@gmail.com>

* integration test

Signed-off-by: Ruihang Xia <waynestxia@gmail.com>

* Update src/servers/src/http/hints.rs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* refactor: with FORMAT option for explain format

* lift some well-known metrics

Signed-off-by: Ruihang Xia <waynestxia@gmail.com>

---------

Signed-off-by: Ruihang Xia <waynestxia@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Ning Sun <sunning@greptime.com>

src/sql/src/statements/explain.rs

@@ -15,7 +15,7 @@
 use std::fmt::{Display, Formatter};
 
 use serde::Serialize;
-use sqlparser::ast::Statement as SpStatement;
+use sqlparser::ast::{AnalyzeFormat, Statement as SpStatement};
 use sqlparser_derive::{Visit, VisitMut};
 
 use crate::error::Error;
@@ -26,6 +26,15 @@ pub struct Explain {
     pub inner: SpStatement,
 }
 
+impl Explain {
+    pub fn format(&self) -> Option<AnalyzeFormat> {
+        match self.inner {
+            SpStatement::Explain { format, .. } => format,
+            _ => None,
+        }
+    }
+}
+
 impl TryFrom<SpStatement> for Explain {
     type Error = Error;