hack: replace go-mod-prepare.sh with wrapper script
- follow-up to (and builds on) https://github.com/moby/moby/pull/44459

**- What I did**
To make the local build environment more correct and consistent, we should never leave an uncommitted go.mod in the tree; however, we need a go.mod for certain commands to work properly. Use a wrapper script to create and destroy the go.mod as needed instead of potentially changing tooling behavior by leaving it.

Also add a script to prevent go.mod from sneaking back in; as we are not a Go module, and cannot currently become one, we want to prevent new contributors from mistakenly trying to turn Moby into one.

**- How to verify it**
Manually, more or less.

**- A picture of a cute animal (not mandatory but encouraged)**
![image](https://user-images.githubusercontent.com/1049222/202741498-2fd212af-9387-4ccb-83a7-69a543254392.png)

.gitignore
# If you want to ignore files created by your editor/tools, please consider a
# [global .gitignore](https://help.github.com/articles/ignoring-files).

*~
*.bak
*.orig
.*.swp
.DS_Store
thumbs.db

# local repository customization
.envrc
.bashrc
.editorconfig

# top-level go.mod is not meant to be checked in
/go.mod
# build artifacts
bundles/
cli/winresources/*/*.syso
cli/winresources/*/winres.json
contrib/builder/rpm/*/changelog

# ci artifacts
*.exe
*.gz
go-test-report.json
junit-report.xml
profile.out
test.main

# If you want to ignore files created by your editor/tools, please consider a
# [global .gitignore](https://help.github.com/articles/ignoring-files).

*~
*.bak
*.orig
.*.swp
.DS_Store
thumbs.db

# local repository customization
.envrc
.bashrc
.editorconfig

# build artifacts
bundles/
cli/winresources/*/*.syso
cli/winresources/*/winres.json
contrib/builder/rpm/*/changelog

# ci artifacts
*.exe
*.gz
go-test-report.json
junit-report.xml
profile.out
test.main

I think a CI check makes more sense than a `.gitignore`, ignoring the go.mod is problematic because it may mask behavior changes from a go.mod file that appears from some other source.