Update Ads7138 (alert pin example, thread safety)

[finger563]

Description

• Changed the event / alert checking to actually use GPIO ISR + task, with the ALERT pin connected to A0 of the QtPy
• Updated ads7138 to have mutex protecting access to ensure thread safety
• Updated sdkconfig to have 1 khz RTOS and 240 MHz processor clock
• Updated example to configure the alert pin explicitly
• Updated docs (readme)
• Rebuild docs (html)

Motivation and Context

It's always good to have examples more representative of real code - so we moved the event flag checking to actually happen when the alert pin triggers (and updated the docs / test bench to connect the ALERT pin to the QtPy).

How has this been tested?

Building and running the updated example.

Screenshots (if appropriate, e.g. schematic, board, console logs, lab pictures):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Hardware (schematic, board, system design) change
• Software change

Checklist:

• My change requires a change to the documentation.
• I have added / updated the documentation related to this change via either README or WIKI

Software

• I have added tests to cover my changes.
• I have updated the .github/workflows/build.yml file to add my new test to the automated cloud build github action.
• All new and existing tests passed.
• My code follows the code style of this project.