Revamp FTP Listener logic

[Maninda]

Purpose

Resolves ballerina-platform/ballerina-library#1703

Checklist

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

[codecov]

Codecov Report

Merging #381 (35f37bd) into master (79d724f) will increase coverage by 0.00%.
The diff coverage is 59.37%.

@@            Coverage Diff            @@
##             master     #381   +/-   ##
=========================================
  Coverage     81.95%   81.95%           
- Complexity      179      185    +6     
=========================================
  Files            29       29           
  Lines          1097     1103    +6     
  Branches        163      163           
=========================================
+ Hits            899      904    +5     
+ Misses          145      144    -1     
- Partials         53       55    +2     

Impacted Files	Coverage Δ
...ftp/transport/server/RemoteFileSystemConsumer.java	64.64% <14.28%> (ø)
...tractimpl/RemoteFileSystemServerConnectorImpl.java	70.00% <45.45%> (-5.00%)	⬇️
...va/io/ballerina/stdlib/ftp/server/FtpListener.java	74.57% <51.72%> (-0.43%)	⬇️
ballerina/external_functions.bal	100.00% <100.00%> (ø)
ballerina/listener_endpoint.bal	93.18% <100.00%> (+2.27%)	⬆️
...ballerina/stdlib/ftp/server/FtpListenerHelper.java	77.77% <100.00%> (+3.58%)	⬆️
...ort/impl/RemoteFileSystemConnectorFactoryImpl.java	100.00% <100.00%> (ø)

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