Update "Ingest logs from a Python application using Filebeat” (#1965)

In this PR:

- Restructured document to follow a more logical structure and flow
- Removed (unnecessary) references to ECE
- Updated outdated info related to UI changes
- Updated outdated info related to the Filebeat config: replaced
deprecated `log` input type with the `filestream` input type and
adjusted the config options accordingly
- Updated the screenshots (removed outdated Donut chart)
- Promoted bold “titles” of sections to headers
- Fixed formatting, typos, and style issues

Closes [#1640](#1640) and
[#125444]( elastic/cloud#125444)

Author: vishaangelova