sphinx-reredirects redirect for mc admin top (#1027)

Add `sphinx-reredirects` extension and create a redirect for the former
`reference/minio-mc-admin/mc-admin-top.rst`.

To install locally:
```
pip3 install sphinx-reredirects
```
To test:
- Go to the old URL.
- You are redirected to the new deprecated URL.

Example:
```
http://192.241.195.202:9000/staging/DOCS-896-redirects/linux/reference/minio-mc-admin/mc-admin-top.html
```
redirects to
```
http://192.241.195.202:9000/staging/DOCS-896-redirects/linux/reference/deprecated/mc-admin-top.html
```


The redirect is server-side, browser without JS still gets the correct
redirected page.

source/default-conf.py

@@ -43,6 +43,7 @@ extensions = [
     'myst_parser',
     'sphinx_design',
     'sphinx.ext.intersphinx',
+    'sphinx_reredirects',
 ]
 
 # -- External Links
@@ -195,6 +196,14 @@ images_config = {
    'override_image_directive' : True
 }
 
+# sphinx-reredirects redirect rules
+# `.rst` for source assumed in the rules
+# `.html` for target must be included
+redirects = {
+    "reference/minio-mc-admin/mc-admin-top": "../deprecated/mc-admin-top.html"
+}
+
+
 # -- Options for HTML output -------------------------------------------------
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for