Fix format for "datetime" context (config description parameter)

The new expected format is "YYYY-MM-DD hh:mm:ss" instead of "YYYY-MM-DD hh:mm" as previously documented.

The "datetime" context is currently not used by official bindings and this context value is also not yet supported by Main UI.

Signed-off-by: Laurent Garnier <lg.hc@free.fr>

developers/addons/config-xml.md

@@ -117,7 +117,7 @@ The following contexts require a specific format of the content:
  <tr><td>password-create</td><td>text</td><td>alphanumeric characters</td><td>custom password input</td></tr>
  <tr><td>color</td><td>text</td><td>#000000 - #ffffff (hex color)</td><td><code>&lt;input type="color"/></code></td></tr>
  <tr><td>date</td><td>text</td><td>YYYY-MM-DD</td><td><code>&lt;input type="date"/></code></td></tr>
- <tr><td>datetime</td><td>text</td><td>YYYY-MM-DD hh:mm</td><td>custom input field</td></tr>
+ <tr><td>datetime</td><td>text</td><td>YYYY-MM-DD hh:mm:ss</td><td>custom input field</td></tr>
  <tr><td>email</td><td>text</td><td>username@domain.com</td><td><code>&lt;input type="email"/></code></td></tr>
  <tr><td>month</td><td>text</td><td>month of year</td><td>custom input field</td></tr>
  <tr><td>week</td><td>integer</td><td>week of year</td><td>custom input field</td></tr>