change fixed version to replace string (#2506)

* change fixed version to replace string

Signed-off-by: Kosuke Morimoto <ksk@vdaas.org>

* Update docs/overview/component/agent.md

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
Signed-off-by: Kosuke Morimoto <kou.morimoto@gmail.com>

---------

Signed-off-by: Kosuke Morimoto <ksk@vdaas.org>
Signed-off-by: Kosuke Morimoto <kou.morimoto@gmail.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

docs/overview/component/agent.md

@@ -74,9 +74,9 @@ You have to wait to complete the CreateIndex and SaveIndex functions before sear
 
 This image shows the mechanism to create NGT index.
 
-<img src="../../../assets/docs/overview/component/agent/ngt.png" />
+<img src="../../../assets/docs/overview/component/agent/ngt.png" alt="NGT Index Creation Mechanism" />
 
-Please refer to [Go Doc](https://pkg.go.dev/github.com/vdaas/vald@v1.3.1/pkg/agent/core/ngt/service) for other functions.
+Please refer to [Go Doc](https://pkg.go.dev/github.com/vdaas/vald@VERSION@/pkg/agent/core/ngt/service) for other functions.
 
 #### Vald Agent Faiss