[BUG] Orchestrion fails to run outside of go module tree

[eliottness]

Describe what happened:

Orchestrion fails to run standalone binary outside of a go.mod tree

Describe what you expected:

I would expect the package to run and build fine.

Steps to reproduce the issue:

❯ cd /tmp
❯ go run github.com/gohugoio/hugo@latest --help
[... outputs the help test ...]

❯ orchestrion go run github.com/gohugoio/hugo@latest       
╭──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│                                                                                                                      │
│  Warning: github.com/DataDog/orchestrion is not present in your go.mod file.                                         │
│  In order to ensure build reliability and reproductibility, orchestrion will now add itself in your go.mod file by:  │
│                                                                                                                      │
│      1. creating a new file named orchestrion.tool.go                                                                │
│      2. running go get github.com/DataDog/orchestrion@v1.0.0                                                         │
│      3. running go mod tidy                                                                                          │
│                                                                                                                      │
│  You should commit the resulting changes into your source control system.                                            │
│                                                                                                                      │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
Failed to pin orchestrion in go.mod: getting GOMOD: in "/tmp": `go env GOMOD` returned a blank string

Additional environment details (Version of Go, Operating System, etc.):
Version of orchestrion: v1.0.0
Tested on MacOS and Linux
Also fails the same in TOOLEXEC and GOFLAGS mode in addition with the DRIVER mode of orchestrion

[RomainMuller]

Off the bat, I' don't think this is a use-case we can support (we should probably refrain from making modifications into the GOMODCACHE tree)...

I guess the best way forward (short of a breakthrough idea) is to detect this and gracefully fail (providing an explanation).

[eliottness]

One of orchestrion underlying features is injecting dependencies at link time since the go toolchain does not allow us to do it in a cooperative way. But resolving these new dependencies without a go.mod and go.sum db available create issues like #433

Therefore we decided to delay this feature for an undetermined about of time. Feel free to like a 👍 on this comment if you came across this asking for this specific feature.