ci: use gci linter (#5708)

* use gofmput to format code

* use gci to format imports

* reconfigure gci

* linter autofixes

* rearrange imports a little

* export GOOS=windows golangci-lint run ./... --fix

.golangci.yml

@@ -2,12 +2,26 @@ linters-settings:
   errcheck:
     ignore: fmt:.*,go.uber.org/zap/zapcore:^Add.*
     ignoretests: true
+  gci:
+    sections:
+      - standard # Standard section: captures all standard packages.
+      - default # Default section: contains all imports that could not be matched to another section type.
+      - prefix(github.com/caddyserver/caddy/v2/cmd) # ensure that this is always at the top and always has a line break.
+      - prefix(github.com/caddyserver/caddy) # Custom section: groups all imports with the specified Prefix.
+    # Skip generated files.
+    # Default: true
+    skip-generated: true
+    # Enable custom order of sections.
+    # If `true`, make the section order the same as the order of `sections`.
+    # Default: false
+    custom-order: true
 
 linters:
   disable-all: true
   enable:
     - bodyclose
     - errcheck
+    - gci
     - gofumpt
     - gosec
     - gosimple
@@ -76,23 +90,23 @@ output:
 issues:
   exclude-rules:
     # we aren't calling unknown URL
-    - text: "G107" # G107: Url provided to HTTP request as taint input
+    - text: 'G107' # G107: Url provided to HTTP request as taint input
       linters:
         - gosec
     # as a web server that's expected to handle any template, this is totally in the hands of the user.
-    - text: "G203" # G203: Use of unescaped data in HTML templates
+    - text: 'G203' # G203: Use of unescaped data in HTML templates
       linters:
         - gosec
     # we're shelling out to known commands, not relying on user-defined input.
-    - text: "G204" # G204: Audit use of command execution
+    - text: 'G204' # G204: Audit use of command execution
       linters:
         - gosec
     # the choice of weakrand is deliberate, hence the named import "weakrand"
     - path: modules/caddyhttp/reverseproxy/selectionpolicies.go
-      text: "G404" # G404: Insecure random number source (rand)
+      text: 'G404' # G404: Insecure random number source (rand)
       linters:
         - gosec
     - path: modules/caddyhttp/reverseproxy/streaming.go
-      text: "G404" # G404: Insecure random number source (rand)
+      text: 'G404' # G404: Insecure random number source (rand)
       linters:
         - gosec