Fix indentation in default devbox config

[humtta]

Summary

DefaultConfig() defines the default configuration using a raw string literal directly in the function body. Because raw string literals in Go preserve all whitespace, the resulting JSON ends up with extra leading spaces on almost every line.

This fix extracts the template into a package-level const, so the string starts at column zero and the resulting JSON is well-formed.

devbox.json before the change:

{␊
····"$schema":·"https://raw.githubusercontent.com/jetify-com/devbox/main/.schema/devbox.schema.json",␊
····"packages":·[],␊
····"shell":·{␊
······"init_hook":·[␊
········"echo·'Welcome·to·devbox!'·>·/dev/null"␊
······],␊
······"scripts":·{␊
········"test":·[␊
··········"echo·\"Error:·no·test·specified\"·&&·exit·1"␊
········]␊
······}␊
····}␊
··}␊
··

devbox.json after the change:

{␊
··"$schema":·"https://raw.githubusercontent.com/jetify-com/devbox/main/.schema/devbox.schema.json",␊
··"packages":·[],␊
··"shell":·{␊
····"init_hook":·[␊
······"echo·'Welcome·to·devbox!'·>·/dev/null"␊
····],␊
····"scripts":·{␊
······"test":·[␊
········"echo·\"Error:·no·test·specified\"·&&·exit·1"␊
······]␊
····}␊
··}␊
}␊

How was it tested?

Ran devbox init locally and inspected the generated devbox.json before and after the change.

Community Contribution License

All community contributions in this pull request are licensed to the project maintainers under the terms of the Apache 2 License.

By creating this pull request, I represent that I have the right to license the contributions to the project maintainers under the Apache 2 License as stated in the Community Contribution License.