Option to de/activate Esbonio registration

[danwos]

With our new VsCode extension we now have a standalone extension, which does not need to register anything in esbonio.

The feature set is the same so that both ways can make trouble.

Therefore the Sphinx-Needs esbonio integration gets deprecated with version 2.0 and it should be possible to reactive the automatic registration so that the new extension can be used.

Tasks:

• Add a DeprecationWarning, if esbonio registration is used and gets activated.
• Add option needs_support_esbonio, which is default True for version <2.0