feat(pg,redis): add --as flag to pg:promote and redis:promote (W-23597911, #1819)

[heroku-johnny]

Summary

• Adds --as NAME flag to heroku pg:promote — allows creating the promoted database attachment under a custom name instead of the hardcoded DATABASE
• Adds --as NAME flag to heroku redis:promote — allows creating the promoted Key-Value Store attachment under a custom name instead of the hardcoded REDIS
• When --as is omitted both commands fall back to the original default names, so existing behavior is unchanged
• Follows the same flags.as pattern already established in addons:attach and pg:connection-pooling:attach

Resolves GUS W-23597911 / GitHub #1819

Test plan

• pg:promote unit tests pass, including new test for --as CUSTOM_DB which asserts the attachment POST sends name: 'CUSTOM_DB'
• redis:promote unit tests pass, including new test for --as CUSTOM_REDIS which asserts the attachment POST sends name: 'CUSTOM_REDIS'
• ESLint passes with zero new errors on changed files
• heroku pg:promote --app <app> <db> --as STAGING_DB creates attachment named STAGING_DB_URL
• heroku redis:promote --app <app> <redis> --as STAGING_REDIS creates attachment named STAGING_REDIS_URL
• Omitting --as still promotes to DATABASE_URL / REDIS_URL as before

🤖 Generated with Claude Code

[michaelmalave]

Nice! Testing successful and code passes checks. LGTM!