Co-authored-by: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>

This patch implements support for secret-less OIDC-based publishing to
PyPI-like package indexes. The OIDC flow is activated when neither
username, nor password action inputs are set.

The OIDC "token exchange," is an authentication technique that PyPI
(and TestPyPI, and hopefully some future others) supports as an
alternative to long-lived username/password combinations or API
tokens.

OIDC token exchange boils down to the following set of steps:

1. A user (currently only someone in the OIDC beta on PyPI) configured
   a particular GitHub Actions workflow in their repository as a
   trusted OIDC publisher;
2. That workflow uses this action to mint an OIDC token;
3. That OIDC token is sent to PyPI (or another index), which exchanges
   it for a temporary API token;
4. That API token is used as normal.

For the seamless configuration-free upload to work, the end-users are
expected to explicitly assign the `id-token: write` privilege to the
auto-injected `GITHUB_TOKEN` secret on the job level. They should also
set up GHA workflow trust on the PyPI side.

PyPI's documentation: https://pypi.org/help/#openid-connect
Beta test enrollment: pypi/warehouse#12965

close: #130

This patch fixes the default PyPI upload URL in the action metadata — a regression that happened in v1.8.0.

Signed-off-by: William Woodruff <william@trailofbits.com>

oidc-exchange: avoid splitting the error message

Signed-off-by: William Woodruff <william@trailofbits.com>

Co-authored-by: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>

This patch improves the logging detalization of which authentication
mode is selected when the action runs. It uses the `::notice` workflow
command to surface this detail to the workflow run summary page as
annotations.