Implemented support for confluence page labels

[OlegKarasik]

This PR adds support for setting page labels specified as part of command line arguments.

Here is an example (which will create a page with two labels 'azure' and 'dotnet').

python ... --label azure --label dotnet

There is no need to specify labels on subsequent page updates (previous labels will persist on the page).

Introduced parameters:	Name	Description
--labels	can be specified multiple times, each time it specifies a separate label