Rest API documentation link in File System API documentation page doesn't work

**Alluxio Version:**

https://docs.alluxio.io/os/user/edge/en/api/FS-API.html



**Describe the bug**

The link to "Rest API documentation" doesn't work on the above page.

The link on master works. The link is generated as [REST API documentation](https://docs.alluxio.io/os/restdoc/{{site.ALLUXIO_MAJOR_VERSION}}/proxy/index.html)



Is there a more reliable way to make sure this works?



I double checked 2.7.4 documentation, which redirects to https://docs.alluxio.io/os/restdoc/stable/master/index.html



The word "master" in the link also makes me wonder whether this is the right version to link to.



**To Reproduce**

Go to https://docs.alluxio.io/os/user/edge/en/api/FS-API.html, search for "REST API documentation", click on the link,

which brings you to https://docs.alluxio.io/os/restdoc/edge/proxy/index.html, which is almost empty.



**Expected behavior**

Compare to https://docs.alluxio.io/os/restdoc/stable/master/index.html which has detailed descriptions of apis.



**Urgency**

I don't know.



**Are you planning to fix it**

No, I don't know how to fix this.

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