[Feature] - Return permission denied rather than server error upon attempted PUT on ro-fs

[Ostheer]

Describe the solution you'd like
Some of my buckets are mounted read-only.
When a user tries to PUT something there, they receive an internal server error.
It would be nice if they got some sort of Permission Denied error instead.

Server log when I try it now:

2025/02/10 16:56:06 Internal Error, open temp file: make temp dir: mkdir bucketname/.sgwtmp: read-only file system
16:56:06 | 500 |     131.086µs | 172.17.0.1 | PUT | /bucketname/raw/project1/file3 | - |
16:56:23 | 500 |     171.091µs | 172.17.0.1 | PUT | /bucketname/raw/project1/file3 | - |

[benmcclelland]

Maybe this error would be more appropriate in this case?

	ErrMethodNotAllowed: {
		Code:           "MethodNotAllowed",
		Description:    "The specified method is not allowed against this resource.",
		HTTPStatusCode: http.StatusMethodNotAllowed,
	},

[Ostheer]

Yes, that seems to cover it quite well!
I suppose the same message can be used for other attempted write actions (e.g. moving, renaming).