feat: add speakeasy configure dependabot command

[AshGodfrey]

Summary

Adds a new speakeasy configure dependabot command that creates or updates a .github/dependabot.yml file to automate dependency updates for SDK repositories.

Features

Standalone Command

speakeasy configure dependabot
speakeasy configure dependabot -d /path/to/workflow

Auto-prompt After GitHub Setup

After speakeasy configure github completes successfully, users are prompted:

Would you also like to configure Dependabot for automated dependency updates?
> Yes
  No

Smart Merge

• Reads existing dependabot.yml if present
• Preserves user customizations (groups, ignore rules, registries, custom schedules)
• Only adds missing ecosystems
• Shows helpful messages:
  • "Successfully created dependabot.yml" (new file)
  • "Successfully updated dependabot.yml - Added ecosystems: npm, pip" (merge)
  • "dependabot.yml already has all needed ecosystems configured" (nothing to add)

Auto-detection of SDK Targets

Reads .speakeasy/workflow.yaml and maps targets to dependabot ecosystems:

Speakeasy Target	Dependabot Ecosystem
typescript, mcp-typescript	npm
python	pip
go	gomod
java	maven
csharp	nuget
php	composer
ruby	bundler
terraform	terraform

github-actions is always included.

Example Output

For a workflow with TypeScript and Python targets:

version: 2
updates:
  - package-ecosystem: github-actions
    directory: /
    schedule:
      interval: weekly
  - package-ecosystem: npm
    directory: /
    schedule:
      interval: weekly
  - package-ecosystem: pip
    directory: /
    schedule:
      interval: weekly

Implementation Notes

• Follows existing patterns in configure.go
• Reuses ConfigureGithubFlags for the -d flag
• Uses same YAML encoding approach as other workflow generators
• Inline type definitions (consistent with other single-use types)
• Uses yaml:",inline" to preserve unknown fields during merge

Testing

Tested locally:

• ✅ Creates new dependabot.yml with detected ecosystems
• ✅ Merges with existing file, preserving customizations
• ✅ Shows appropriate messages for each scenario
• ✅ Prompt appears after configure github
• ✅ Builds successfully