feat(config): add base implementation

* feat(config): naive implementation

feat(config): get command for a run from config

* docs: add config

* fix typo [skip ci]

* test: add config

spec/gopher_config_spec.lua

@@ -0,0 +1,41 @@
+describe("gopher.config", function()
+  it("can be required", function()
+    require "gopher.config"
+  end)
+
+  it(".setup() when gets empty table not edit config", function()
+    local c = require "gopher.config"
+    c.setup {}
+
+    assert.are.same(c.config.commands.go, "go")
+    assert.are.same(c.config.commands.gomodifytags, "gomodifytags")
+    assert.are.same(c.config.commands.gotests, "gotests")
+    assert.are.same(c.config.commands.impl, "impl")
+  end)
+
+  it(".setup() when get one custom value sets that", function()
+    local c = require "gopher.config"
+    c.setup { commands = {
+      go = "custom_go",
+    } }
+
+    assert.are.same(c.config.commands.go, "custom_go")
+  end)
+
+  it(".setup() when get all custom values sets it", function()
+    local c = require "gopher.config"
+    c.setup {
+      commands = {
+        go = "go1.18",
+        gomodifytags = "user-gomodifytags",
+        gotests = "gotests",
+        impl = "goimpl",
+      },
+    }
+
+    assert.are.same(c.config.commands.go, "go1.18")
+    assert.are.same(c.config.commands.gomodifytags, "user-gomodifytags")
+    assert.are.same(c.config.commands.gotests, "gotests")
+    assert.are.same(c.config.commands.impl, "goimpl")
+  end)
+end)