Cronvoy: support pinned Certificates

The Cronet API supports the pinning of certificates: **[```CronetEngine.Builder.addPublicKeyPins```](https://source.chromium.org/chromium/chromium/src/+/main:components/cronet/android/api/src/org/chromium/net/CronetEngine.java;l=243)**

```
/**
*

* Pins a set of public keys for a given host. By pinning a set of public keys,
* {@code pinsSha256}, communication with {@code hostName} is required to
* authenticate with a certificate with a public key from the set of pinned ones.
* An app can pin the public key of the root certificate, any of the intermediate
* certificates or the end-entry certificate. Authentication will fail and secure
* communication will not be established if none of the public keys is present in the
* host's certificate chain, even if the host attempts to authenticate with a
* certificate allowed by the device's trusted store of certificates.
*

*

* Calling this method multiple times with the same host name overrides the previously
* set pins for the host.
*

*

* More information about the public key pinning can be found in
* RFC 7469.
*

*
* @param hostName name of the host to which the public keys should be pinned. A host that
* consists only of digits and the dot character is treated as invalid.
* @param pinsSha256 a set of pins. Each pin is the SHA-256 cryptographic
* hash of the DER-encoded ASN.1 representation of the Subject Public
* Key Info (SPKI) of the host's X.509 certificate. Use
* {@link java.security.cert.Certificate#getPublicKey()
* Certificate.getPublicKey()} and
* {@link java.security.Key#getEncoded() Key.getEncoded()}
* to obtain DER-encoded ASN.1 representation of the SPKI.
* Although, the method does not mandate the presence of the backup pin
* that can be used if the control of the primary private key has been
* lost, it is highly recommended to supply one.
* @param includeSubdomains indicates whether the pinning policy should be applied to
* subdomains of {@code hostName}.
* @param expirationDate specifies the expiration date for the pins.
* @return the builder to facilitate chaining.
* @throws NullPointerException if any of the input parameters are {@code null}.
* @throws IllegalArgumentException if the given host name is invalid or {@code pinsSha256}
* contains a byte array that does not represent a valid
* SHA-256 hash.
*/
public Builder addPublicKeyPins(String hostName, Set pinsSha256,
boolean includeSubdomains, Date expirationDate)
```

Even though this feature is discouraged, not honoring it would presumably break some App Developers.