feat(df): add maven wrapper command behind the firewall proxy

Michael Eddingtonrequested to merge
df-mr-11-maven-commands into main

Adds the Maven ecosystem, making glab dependency-firewall maven usable end-to-end behind the firewall proxy.

  • MavenMatcher recognizes Maven artifact downloads and uploads by the repository path shape and maps them to a maven policy coordinate.
  • The maven package manager implements the interface; it trusts the proxy through the JVM PKCS#12 truststore helper (jvmtrust), pointing MAVEN_OPTS at a generated store rather than an env-named CA file.
  • The df maven wrapper forwards all arguments verbatim to mvn.

Stacked on !3839 (merged) (the A→B→C command chain) and depends on the jvmtrust helper in !3840 (merged); this branch carries both until they merge. Gradle reuses this matcher and lands in a follow-up MR to keep each slice small.

Testing

  • go build ./...
  • GITLAB_CI=true go test ./internal/commands/df/... ./internal/dependencyfirewall/... — matcher download/upload recognition, manager metadata/matcher type, JVM truststore trust (proxy CA present even when not first in the bundle).
  • gofmt and golangci-lint clean.
  • make gen-docs regenerated the maven doc page.

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