feat: golangci-lint configuration

Oversight on my part, this was never added originally. This gives us
much stronger linter rules by default.

templates/.golangci.yml.tpl

@@ -0,0 +1,69 @@
+# yaml-language-server: $schema=https://json.schemastore.org/golangci-lint
+
+# Linter settings
+linters-settings:
+  errcheck:
+    check-blank: true
+  gocyclo:
+    min-complexity: 25
+  gocritic:
+    enabled-tags:
+      - diagnostic
+      - experimental
+      - opinionated
+      - performance
+      - style
+  lll:
+    line-length: 140
+
+linters:
+  # Inverted configuration with enable-all and disable is not scalable
+  # during updates of golangci-lint.
+  disable-all: true
+  enable:
+    - bodyclose
+    - dogsled
+    - errcheck
+    - errorlint
+    - exhaustive
+    - exportloopref
+    - gochecknoinits
+    - gocritic
+    - gocyclo
+    - gofmt
+    - goheader
+    - goimports
+    - gosec
+    - gosimple
+    - govet
+    - ineffassign
+    - lll
+    - misspell
+    - nakedret
+    - staticcheck
+    - revive
+    - typecheck
+    - unconvert
+    - unparam
+    - unused
+    - whitespace
+
+issues:
+  exclude:
+    # We allow error shadowing
+    - 'declaration of "err" shadows declaration at'
+
+  # Excluding configuration per-path, per-linter, per-text and per-source
+  exclude-rules:
+    # Exclude some linters from running on tests files.
+    - path: _test\.go
+      linters:
+        - errcheck
+        - funlen
+        - gochecknoglobals # Globals in test files are tolerated.
+        - gocyclo
+        - goheader # Don't require license headers in test files.
+        - gosec
+
+output:
+  sort-results: true