added google analytics global tag for docs

[Priyansi]

Description:

As discussed earlier with @vfdev-5 this will give us detailed insights into the documentation experience of the user and the suitable place to add this tag was discussed with @ydcjeff.

Also according to this article under Dynamic website -

Link the include file so that the snippet appears before the closing tag on every webpage you want to measure.

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[ydcjeff]

LGTM.
Before merging, please confirm we are getting any traffic by visiting the preview link.

[Priyansi]

LGTM.
Before merging, please confirm we are getting any traffic by visiting the preview link.

@vfdev-5 since you have the access to the dashboard, can you please confirm this?

[vfdev-5]

Thanks a lot, @Priyansi !