[#1388] golangci: Make unused linter stricker

Add aditional checks. The most important false positive - structs used as
map keys.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

.golangci.yml

@@ -38,6 +38,10 @@ linters-settings:
     alias:
       pkg: git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object
       alias: objectSDK
+  unused:
+    field-writes-are-uses: false
+    exported-fields-are-used: false
+    local-variables-are-used: false
   custom:
     truecloudlab-linters:
       path: bin/linters/external_linters.so