update rust quickstarter MSRV and boilerplate refactor and docs

[gerardcl]

In this update, part of a recurrent series of maintenance and improvements for the Rust Axum Quickstarter, we are:

• updating the MSRV to 1.79.0
• update CICD agent dependencies
• align use of nextest also with llvm-cov codegen (ensuring isolated process per test case run)
• refactor for better tracing/logging support with official RUST_LOG config
• enable better automated settings handling with .env files support
• enable temporal environment variables overwriting for test case runs

Tasks:

• [x] Updated documentation in docs/modules/... directory
• [x] Ran tests in <quickstarter>/testdata directory

[braisvq1996]

@gerardcl I wil use golden test tomorow to verify it still works and get bak to you

[braisvq1996]

tests for the new Quickstarter version went though

[gerardcl]

@FLIGHTLAMA @braisvq1996 @kuebler ready, do final check, and, maybe, approve! 👍