Allow setting the webAllowOthers from the application.properties

[mdeinum]

I work for different clients and it is handy to have the H2 Console at hand to work with the embedded database. However I use a lot of VMs (using Vagrant for instance) and when accessing the h2console it gives an exception that you cannot connect. Setting the webAllowOthers to true fixes this.

However it requires to either re-register the bean or define a BeanPostProcessor to be able to set this property. If would be nice if we could add spring.h2.console.web-allow-others=true (default would be `false) and that it then would be set as an init parameter for the servlet.

[snicoll]

Closing in favour of the PR #5417 - @mdeinum if you intend to submit a PR, you don't need to create an issue. Thanks.