CCIP-4464: Add POST requests support in token data http client (#1556)

## Motivation
[CCIP-4464](https://smartcontract-it.atlassian.net/browse/CCIP-4464)

## Solution

core/services/ocr2/plugins/ccip/tokendata/http/http_client.go

@@ -22,11 +22,11 @@ type IHttpClient interface {
 type HttpClient struct {
 }
 
-func (s *HttpClient) Get(ctx context.Context, url string, timeout time.Duration) ([]byte, int, http.Header, error) {
+func doRequest(ctx context.Context, url string, requestType string, requestBody io.Reader, timeout time.Duration) ([]byte, int, http.Header, error) {
 	// Use a timeout to guard against attestation API hanging, causing observation timeout and failing to make any progress.
 	timeoutCtx, cancel := context.WithTimeoutCause(ctx, timeout, tokendata.ErrTimeout)
 	defer cancel()
-	req, err := http.NewRequestWithContext(timeoutCtx, http.MethodGet, url, nil)
+	req, err := http.NewRequestWithContext(timeoutCtx, requestType, url, requestBody)
 	if err != nil {
 		return nil, http.StatusBadRequest, nil, err
 	}
@@ -50,7 +50,10 @@ func (s *HttpClient) Get(ctx context.Context, url string, timeout time.Duration)
 	return body, res.StatusCode, res.Header, err
 }
 
-func (s *HttpClient) Post(ctx context.Context, url string, requestData io.Reader, timeout time.Duration) ([]byte, int, http.Header, error) {
-	// TODO: Implement
-	return nil, 0, nil, nil
+func (s *HttpClient) Get(ctx context.Context, url string, timeout time.Duration) ([]byte, int, http.Header, error) {
+	return doRequest(ctx, url, http.MethodGet, nil, timeout)
+}
+
+func (s *HttpClient) Post(ctx context.Context, url string, requestBody io.Reader, timeout time.Duration) ([]byte, int, http.Header, error) {
+	return doRequest(ctx, url, http.MethodPost, requestBody, timeout)
 }