refactor: Change config section and key string literals into constants (#7095)

Co-authored-by: Bart <11445373+bthomee@users.noreply.github.com>

src/test/jtx/Env_test.cpp

@@ -35,6 +35,7 @@
 #include <xrpl/beast/hash/uhash.h>
 #include <xrpl/beast/unit_test/suite.h>
 #include <xrpl/beast/utility/Journal.h>
+#include <xrpl/config/Constants.h>
 #include <xrpl/json/json_value.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/ErrorCodes.h>
@@ -863,7 +864,7 @@ public:
             jtx::Env const env{
                 *this,
                 jtx::envconfig([](std::unique_ptr<Config> cfg) {
-                    (*cfg).deprecatedClearSection("port_rpc");
+                    (*cfg).deprecatedClearSection(Sections::kPortRpc);
                     return cfg;
                 }),
                 nullptr,