Create a new v1.7.3 release of Secretless

[izgeri]

There is a new release of Secretless that includes the version bump of authn-k8s client to 0.19.0 in #1375 and the fix to PostgreSQL SSL mode handling in #1377.

Note that the changelog entry for the fix in #1377 is not quite accurate - we should revise it to:

### Fixed
- Secretless now sends a valid "SSL is not supported" response per the PostgreSQL protocol standard when a client attempts to open an SSL connection (i.e. when configured with SSL mode `require` or `prefer`) via the PostgreSQL connector. When the client is configured with SSL mode `prefer`, the updated response enables the client to downgrade to an insecure connection and continue. Previously, clients sending requests using either `require` or `prefer` SSL mode would receive a generic error from Secretless, which made it harder to determine the root cause of the problem and broke how `prefer` is expected to work.

AC:

• The CHANGELOG in the version bump PR has been reviewed to ensure it meets
  our standards
  and captures the changes in the release.
• The manual tests have been run for the code on master in the version bump
  PR.
• There is a new Secretless tag for the set of changes on master.
• There is a github prerelease for the tag that includes a copy/paste of the
  change log and includes attached artifacts produced in the tag pipeline by
  goreleaser.
• The changeset has been reviewed with the Quality Architect to determine if
  any performance tests (short- or long-term) are required for this set of
  changes.
• Any open docs issues for the changes included in the release have been
  made and are ready to be published.
• If the docs are published and the performance tests aren't needed or are
  complete and passing, then the github release is moved from a prerelease
  to a full release, and a new stable image is produced as a copy of the
  new tag and pushed to DockerHub.