docs: remove bounty policy in favor of governance funding docs (#11789)

The issue bounty program described in docs/bounty.md was never run in
practice. Remove the bounty policy page and its navigation entry, and
update the CONTRIBUTING sponsorship section to point to the current
funding and governance documents in the testcontainers/.github repo,
which describe how sponsorship money is raised and distributed.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: kiview

CONTRIBUTING.md

@@ -8,6 +8,6 @@ There are additional docs describing [contributing documentation changes](./docs
 
 Testcontainers is [in the GitHub Sponsors program](https://github.com/sponsors/testcontainers)!
 
-This repository is supported by our sponsors, meaning that issues are eligible to have a 'bounty' attached to them by sponsors.
+This repository is supported by our sponsors. If you'd like to support the project, please consider sponsoring us via [GitHub Sponsors](https://github.com/sponsors/testcontainers) or [Open Collective](https://opencollective.com/testcontainers).
 
-Please see [the bounty policy page](https://www.testcontainers.org/bounty) if you are interested, either as a sponsor or as a contributor.
+To learn how funds are raised and distributed, see the [Testcontainers project funding policy](https://github.com/testcontainers/.github/blob/main/FUNDING.md). Financial matters are overseen by the Testcontainers Steering Committee, as described in the [project governance document](https://github.com/testcontainers/.github/blob/main/GOVERNANCE.md).

docs/bounty.md

@@ -137,7 +137,6 @@ nav:
     - Contributing:
           - contributing.md
           - contributing_docs.md
-          - bounty.md
 edit_uri: edit/main/docs/
 extra:
     latest_version: 2.0.5