🚀 Feature Request: Promote SecretServer Provider to Beta

The SecretServer provider has been in an alpha state for some time and has reached a level of maturity and community adoption that warrants promotion to beta stability.

Motivation

Promoting the provider signals to users that it is sufficiently stable for production use, but still subject to potential non-breaking API changes in future releases (in line with the External Secrets Operator stability policy).

Key Reasons for Promotion:

• Stability and Testing: The provider has been stable in its current state, and the recent test coverage has been improved.
• Community Adoption: The provider is actively used by the community, with no major stability-related bugs reported recently.
• Active Maintenance: The provider has a committed maintainer for ongoing support and development. (Please confirm the maintainer, as the PR description mentioned a new one, but I cannot see it in my available context).

Proposed Changes

1. Update the stability-support.md file to change the SecretServer provider's stability level from alpha to beta.
2. Ensure documentation reflects the beta status.