release workflow and email template need to be improved

[bobbai00]

Task Summary

Update release candidate workflow and vote email template:

• Use https://downloads.apache.org/incubator/texera/KEYS as the official KEYS URL (auto-synced from release)
• Remove 'rc' suffix from tarball filename (directory still uses RC suffix)
• Simplify verification instructions in vote email
• Add convenience binaries section to clarify only source release is being voted on

Priority

P2 – Medium

Task Type

• Code Implementation
• DevOps / Deployment