HBASE-26099 Add 3.0.0-alpha-1 to download page (#3507)

Signed-off-by: Yulin Niu <[email protected]>

Author: Apache9

src/site/xdoc/downloads.xml

@@ -43,6 +43,31 @@ under the License.
       <th>Download</th>
       <th>Notices</th>
     </tr>
+    <tr>
+      <td style="test-align: left">
+        3.0.0-alpha-1
+      </td>
+      <td style="test-align: left">
+        2021/07/20
+      </td>
+      <td style="test-align: left">
+        <a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/api_compare_2.0.0_to_3.0.0-alpha-1RC0.html">3.0.0-alpha-1 vs 2.0.0</a>
+      </td>
+      <td style="test-align: left">
+        <a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/CHANGES.md">Changes</a>
+      </td>
+      <td style="test-align: left">
+        <a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/RELEASENOTES.md">Release Notes</a>
+      </td>
+      <td style="test-align: left">
+        <a href="https://www.apache.org/dyn/closer.lua/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-src.tar.gz">src</a> (<a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-src.tar.gz.sha512">sha512</a> <a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-src.tar.gz.asc">asc</a>) <br />
+        <a href="https://www.apache.org/dyn/closer.lua/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-bin.tar.gz">bin</a> (<a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-bin.tar.gz.sha512">sha512</a> <a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-bin.tar.gz.asc">asc</a>) <br />
+        <a href="https://www.apache.org/dyn/closer.lua/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-client-bin.tar.gz">client-bin</a> (<a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-client-bin.tar.gz.sha512">sha512</a> <a href="https://downloads.apache.org/hbase/3.0.0-alpha-1/hbase-3.0.0-alpha-1-client-bin.tar.gz.asc">asc</a>)
+      </td>
+      <td>
+        Testing only, not production ready
+      </td>
+    </tr>
     <tr>
       <td style="test-align: left">
         2.4.4