[docs] Switch to conventional commits to automate release notes

[nemesifier]

In order to semi-automate the work needed for creating general release notes (#108), I think we should switch to https://www.conventionalcommits.org/

I would keep the prefix between square brackets as we do now, but use the words indicated there which would help us to generate the release notes.

Blocked by openwisp/openwisp-utils#110 and #109 (these two issues have to be tackled first).

[khush31]

Hey, I would like to work on this issue under your guidance @nemesisdesign and @atb00ker
Should I create another file or updated in the Readme file?

[nemesifier]

@khush31 welcome to the OpenWISP community! I'm sorry, I didn't notice it was not specified in the description that the implementation of this other issue is a pre-requirement for working on this: openwisp/openwisp-utils#110, so we can't proceed now on this, flagging as "blocked". Thank you for your patience. I suggest choosing another issue. We have plenty: https://github.com/orgs/openwisp/projects/12#card-38476438