clang-tidy: Enable readability checks on repo

The readability-* checks in Clang-Tidy focus on improving code
readability by enforcing guidelines and suggesting improvements
that can enhance the clarity and maintainability of C++ code.
This enables readability-const-return-type check.

Change-Id: I4737f07188f6a173678dbe0192914dd5df0dd338
Signed-off-by: Pavithra Barithaya <pavithrabarithaya07@gmail.com>
diff --git a/.clang-tidy b/.clang-tidy
index b21b83b..af74e06 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -241,7 +241,32 @@
 performance-trivially-destructible,
 performance-type-promotion-in-math-fn,
 performance-unnecessary-copy-initialization,
-performance-unnecessary-value-param'
+performance-unnecessary-value-param,
+readability-avoid-const-params-in-decls,
+readability-const-return-type,
+readability-delete-null-pointer,
+readability-deleted-default,
+readability-function-size,
+readability-identifier-naming,
+readability-isolate-declaration,
+readability-make-member-function-const,
+readability-misleading-indentation,
+readability-misplaced-array-index,
+readability-named-parameter,
+readability-non-const-parameter,
+readability-redundant-access-specifiers,
+readability-redundant-function-ptr-dereference,
+readability-redundant-member-init,
+readability-redundant-preprocessor,
+readability-redundant-smartptr-get,
+readability-redundant-string-init,
+readability-simplify-subscript-expr,
+readability-static-accessed-through-instance,
+readability-static-definition-in-anonymous-namespace,
+readability-string-compare,
+readability-suspicious-call-argument,
+readability-uniqueptr-delete-release,
+readability-uppercase-literal-suffix'
 
 WarningsAsErrors: '*'
 HeaderFilterRegex: '.*.hpp'
diff --git a/systemd_target_signal.cpp b/systemd_target_signal.cpp
index 30e5d5b..7698c0e 100644
--- a/systemd_target_signal.cpp
+++ b/systemd_target_signal.cpp
@@ -75,8 +75,8 @@
     }
 }
 
-const std::string SystemdTargetLogging::processError(const std::string& unit,
-                                                     const std::string& result)
+std::string SystemdTargetLogging::processError(const std::string& unit,
+                                               const std::string& result)
 {
     auto targetEntry = this->targetData.find(unit);
     if (targetEntry != this->targetData.end())
diff --git a/systemd_target_signal.hpp b/systemd_target_signal.hpp
index cddb358..4839d55 100644
--- a/systemd_target_signal.hpp
+++ b/systemd_target_signal.hpp
@@ -65,8 +65,8 @@
      *
      * @return valid pointer to error to log, otherwise nullptr
      */
-    const std::string processError(const std::string& unit,
-                                   const std::string& result);
+    std::string processError(const std::string& unit,
+                             const std::string& result);
 
   private:
     /** @brief Start BMC Quiesce Target to indicate critical service failure */