Allow removal for old releases

Hi! I am looking to setup nightly releases for rust-analyzer, and for that I want to publish a github release every night under the same tag. IE, I want the tag itself to move. Looks like at the moment actions-gh-release silently fails in this case:

Release
1s
(node:2749) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 4)
Run softprops/action-gh-release@v1
⬆️ Uploading rust-analyzer-linux...
⬆️ Uploading rust-analyzer-windows.exe...
⬆️ Uploading rust-analyzer-mac...
⬆️ Uploading rust-analyzer.vsix...
🎉 Release ready at https://github.com/matklad/rust-analyzer/releases/tag/2020-03-04
(node:2749) UnhandledPromiseRejectionWarning: HttpError: Validation Failed: {"resource":"ReleaseAsset","code":"already_exists","field":"name"}
    at /home/runner/work/_actions/softprops/action-gh-release/v1/dist/index.js:1:273881
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
(node:2749) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:2749) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:2749) UnhandledPromiseRejectionWarning: HttpError: Validation Failed: {"resource":"ReleaseAsset","code":"already_exists","field":"name"}
    at /home/runner/work/_actions/softprops/action-gh-release/v1/dist/index.js:1:273881
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
(node:2749) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:2749) UnhandledPromiseRejectionWarning: HttpError: Validation Failed: {"resource":"ReleaseAsset","code":"already_exists","field":"name"}
    at /home/runner/work/_actions/softprops/action-gh-release/v1/dist/index.js:1:273881
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
(node:2749) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 3)
(node:2749) UnhandledPromiseRejectionWarning: HttpError: Validation Failed: {"resource":"ReleaseAsset","code":"already_exists","field":"name"}
    at /home/runner/work/_actions/softprops/action-gh-release/v1/dist/index.js:1:273881
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
(node:2749) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 4)

Failing by default is probably the right behavior, but it would be cool if the action had an overwrite: boolean flag to control this behavior

[BotellaA]

@softprops What do you think about this feature? I would love to have an overwrite option!

[greggameplayer]

For me it would also be good to have an overwrite feature