NXCALS-2655 Update docs for standalone python

#Merge request template @acc-logging-team - please have a look for approval.

This MR includes introduction of mkdocs macro plugin. The "variables/substitution text" can be placed as a part of mkdocs.yml configuration file.

An initial idea was to read gradle.properties file, and make available all the properties which are defined there. Unfortunately other plugin: mkdocs-markdownextradata-plugin can ready only yaml files which must placed within docs_dir structure making it difficult to work with gradle.properties.

For simplicity I propose to stay with the simple macro substitution as proposed in this MR.

Closes NXCALS-2655