CDRIVER-4512 remove legacy shell from AWS test scripts (#1514)

* run `setup_secrets.sh` for AWS auth

* use `aws_setup.sh` instead of legacy shell setup for AWS test cases

* remove unused `url_encode`

* make `*.sh` scripts readable and executable in drivers-evergreen-tools

* add `secrets-export.sh` to .gitignore

* remove outdated comment

* remove unnecessary PATH modification

* remove unused `mongodb_bin_dir`

* add shellcheck directives

Ignore `aws_setup.sh` since it is in drivers-evergreen-tools

* add missing `LAMBDA` test case to test without a session token

* migrate Ubuntu 18.04 AWS tasks to Ubuntu 20.04

* migrate 6.0+ tasks to Ubuntu 22.04

* enable tracing and print "aws_auth" trace logs

This is intended to help diagnose spurious observed auth failures

* replace legacy shell with `mongosh` in tutorial