Fix certificate issue. - Githubissues

Used CloseableHttpClient instead of deprecated DefaultHttpClient.
Created SSLContext using the keystore details in the carbon.xml file and added it to the httpClient object.
Added support to configure a proxy.

ASAP

[ ] Is this PR explained thoroughly? All code changes must be accounted for in the PR description.
[ ] Is the PR labeled correctly?

[ ] Are all requirements met? Compare implemented functionality with the requirements specification.
[ ] Does the UI work as expected? There should be no Javascript errors in the console; all resources should load. There should be no unexpected errors. Deliberately try to break the feature to find out if there are corner cases that are not handled.

[ ] Do you fully understand the introduced changes to the code? If not ask for clarification, it might uncover ways to solve a problem in a more elegant and efficient way.
[ ] Does the PR introduce any inefficient database requests? Use the debug server to check for duplicate requests.
[ ] Are all necessary strings marked for translation? All strings that are exposed to users via the UI must be marked for translation.

[ ] Are there sufficient test cases? Ensure that all components are tested individually; models, forms, and serializers should be tested in isolation even if a test for a view covers these components.
[ ] If this is a bug fix, are tests for the issue in place? There must be a test case for the bug to ensure the issue won’t regress. Make sure that the tests break without the new code to fix the issue.
[ ] If this is a new feature or a significant change to an existing feature? has the manual testing spreadsheet been updated with instructions for manual testing?

[ ] Confirm this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.
[ ] Are all UI and API inputs run through forms or serializers?
[ ] Are all external inputs validated and sanitized appropriately?
[ ] Does all branching logic have a default case?
[ ] Does this solution handle outliers and edge cases gracefully?
[ ] Are all external communications secured and restricted to SSL?

[ ] Are changes to the UI documented in the platform docs? If this PR introduces new platform site functionality or changes existing ones, the changes should be documented.
[ ] Are changes to the API documented in the API docs? If this PR introduces new API functionality or changes existing ones, the changes must be documented.
[ ] Are reusable components documented? If this PR introduces components that are relevant to other developers (for instance a mixin for a view or a generic form) they should be documented in the Wiki.

wso2-extensions / identity-outbound-auth-samlsso