Deprecate ES256K Algorithm (#543)

* [SDK-3192] Deprecate secp256k1 curve for EC Algorithms

* Documentation update

Author: poovamraj

lib/src/main/java/com/auth0/jwt/algorithms/Algorithm.java

@@ -183,7 +183,11 @@ public static Algorithm HMAC256(byte[] secret) throws IllegalArgumentException {
      * @param keyProvider the provider of the Public Key and Private Key for the verify and signing instance.
      * @return a valid ECDSA256 Algorithm.
      * @throws IllegalArgumentException if the Key Provider is null.
+     * @deprecated The SECP-256K1 Curve algorithm has been disabled beginning in Java 15.
+     * Use of this method in those unsupported Java versions will throw a {@link java.security.SignatureException}.
+     * This method will be removed in the next major version. See for additional information
      */
+    @Deprecated
     public static Algorithm ECDSA256K(ECDSAKeyProvider keyProvider) throws IllegalArgumentException {
         return new ECDSAAlgorithm("ES256K", "SHA256withECDSA", 32, keyProvider);
     }
@@ -195,7 +199,11 @@ public static Algorithm ECDSA256K(ECDSAKeyProvider keyProvider) throws IllegalAr
      * @param privateKey the key to use in the signing instance.
      * @return a valid ECDSA256 Algorithm.
      * @throws IllegalArgumentException if the provided Key is null.
+     * @deprecated The SECP-256K1 Curve algorithm has been disabled beginning in Java 15.
+     * Use of this method in those unsupported Java versions will throw a {@link java.security.SignatureException}.
+     * This method will be removed in the next major version. See for additional information
      */
+    @Deprecated
     public static Algorithm ECDSA256K(ECPublicKey publicKey, ECPrivateKey privateKey) throws IllegalArgumentException {
         return ECDSA256K(ECDSAAlgorithm.providerForKeys(publicKey, privateKey));
     }