Run gofumpt -w on all go files and integrate with CI

[zalegrala]

What this PR does:

In working in the tempodb package, I notice a few areas that could use a little formatting. Here is a proposal to introduce a bit more opinionated formatting using gofumpt. After review of the changes, this has been integrated into make fmt to apply to the entire codebase.

If we agree on these changes, we could introduce this in tools/ and integrate as part of CI perhaps in a future PR. All editors probably have an auto-formatter as well, but worth checking on your editor. A make target could cover most of us though.

Thoughts?

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[mdisibio]

The changes look fairly unopinionated and ok to me, a little bit cleaner than the default. Main concern is the tooling and preventing churn between contributors. A make target would be great.

[zalegrala]

Those last few commits will do the needful. If this goes to main, make fmt will be required for all committers who don't have their editor configured to use gofumpt as their auto-format.

[mdisibio]

Enabling it to format on save in VS Code was easy following the settings snippet in https://github.com/mvdan/gofumpt#visual-studio-code

However it looks like there isn't a way to include the -extra through gopls, it only has gofumpt: bool. There is a discussion of the rationale in golang/go#56403

[zalegrala]

Thanks for testing @mdisibio. I'm completely open to removing the -extra flag.

[joe-elliott]

i'm good on this as long as everything can be automated on save in popular editors.

we should include details about this tool and how to set it up in ./CONTRIBUTING.md.