Add cert file and mTLS support for JDK11 client

[ldclakmal]

Purpose

This PR add cert file and mTLS support for JDK11 client secure socket configurations. The updated configuration is

public type SecureSocket record {|
    boolean disable = false;
    crypto:TrustStore|string cert;
    crypto:KeyStore|CertKey key?;
|};

public type CertKey record {|
   string certFile;
   string keyFile;
   string keyPassword?;
|};

Fixes ballerina-platform/ballerina-library#936
Related to ballerina-platform/ballerina-library#584

[codecov]

Codecov Report

Merging #137 (aea04bc) into master (b835081) will decrease coverage by 3.03%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master     #137      +/-   ##
============================================
- Coverage     70.56%   67.53%   -3.04%     
- Complexity       97      111      +14     
============================================
  Files            11       11              
  Lines           547      613      +66     
  Branches        272      280       +8     
============================================
+ Hits            386      414      +28     
- Misses          158      192      +34     
- Partials          3        7       +4     

Impacted Files	Coverage Δ	Complexity Δ
.../java/org/ballerinalang/stdlib/jwt/JwksClient.java	47.45% <44.44%> (-16.04%)	18.00 <15.00> (+8.00)	⬇️
jwt-ballerina/jwt_validator.bal	78.07% <100.00%> (+0.07%)	67.00 <0.00> (+4.00)
...ava/org/ballerinalang/stdlib/jwt/JwtConstants.java	90.90% <100.00%> (+90.90%)	1.00 <1.00> (+1.00)
...java/org/ballerinalang/stdlib/jwt/ModuleUtils.java	100.00% <0.00%> (+33.33%)	2.00% <0.00%> (+1.00%)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b835081...aea04bc. Read the comment docs.