Add a new ORT API `GetSessionOptionConfigEntries` (#25277)
### Description
Add a new ORT API `GetSessionOptionConfigEntries`.
### Motivation and Context
#24887 allows plugin-EPs to interface with ORT using a binary stable interface. #24445 allows an EP to handle the extraction of EP options from the session option configurations. For an EP like VitisAI EP to comply with the requirements,
it is necessary for a plugin-EPs to access all config entries in a session option.
```c++
OrtKeyValuePairs * kvps = nullptr;
auto status = GetSessionOptionConfigEntries(session_option, &kvps);
if(status) {
throw status;
}
std::unique_ptr<OrtKeyValuePairs, void (*)(OrtKeyValuePairs*)>
config_entries(kvps,
ort_api.ReleaseKeyValuePairs);
const char* const* keys = nullptr;
const char* const* values = nullptr;
size_t num_keys = 0;
// Get keys and values from the config entries
Ort::GetApi().GetKeyValuePairs(config_entries.get(), &keys, &values, &num_keys);
for (size_t i = 0; i < num_keys; ++i) {
// process keys[i] and values[i]
}
```
