Add OAuth2 JWT bearer grant type support for client

[ldclakmal]

Purpose

This PR adds OAuth2 JWT bearer grant type support for WebSocket client.

Fixes: ballerina-platform/ballerina-library#1788

Examples

import ballerina/io;
import ballerina/websocket;

websocket:Client securedEP = check new("wss://localhost:9090/foo/bar",
    auth = {
        tokenUrl: "https://localhost:9445/oauth2/token",
        assertion: "eyJhbGciOiJFUzI1NiIsImtpZCI6Ij[...omitted for brevity...]",
        clientId: "FlfJYKBD2c925h4lkycqNZlC2l4a",
        clientSecret: "PJz0UhTJMrHOo68QQNpvnqAY_3Aa",
        scopes: ["admin"],
        clientConfig: {
            secureSocket: {
                cert: "../resource/path/to/public.crt"
            }
        }
    },
    secureSocket = {
        cert: "../resource/path/to/public.crt"
    }
);

public function main() returns error? {
    check securedEP->writeTextMessage("Hello, World!");
    string textMessage = check securedEP->readTextMessage();
    io:println(textMessage);
}

Checklist

• Linked to an issue
• Updated the changelog
• Added tests

[codecov]

Codecov Report

Merging #292 (5f38289) into main (9f6b682) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               main     #292   +/-   ##
=========================================
  Coverage     81.37%   81.38%           
  Complexity      351      351           
=========================================
  Files            43       43           
  Lines          2051     2052    +1     
  Branches        318      318           
=========================================
+ Hits           1669     1670    +1     
  Misses          296      296           
  Partials         86       86           

Impacted Files	Coverage Δ
ballerina/auth_types.bal	88.23% <100.00%> (+0.73%)	⬆️

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