Add support for Freshservice Tickets endpoint to API-SDK

[thakurganeshsinghfw]

Changes performed as part of Freshservice API Tickets endpoint support addition

• Modified Freshservice API Specs for generating client stub classes
• Added mew API spec from Stoplight
• Performed required changes to generate client side libraries
• Updated generate.sh and other files to add CLI options
• Built and generated client side libraries
• Updated /docs/README.md and /docs/get-started.md
• Added new directory and files under /src/freshservice
• Updated typedoc.json
• Added new directory and files under /docs/freshservice/
• Updated vuepress config file /docs/.vuepress/config.js
• Added new test suite directory /test/freshservice/
• Added nock unit test suites under /test/freshservice/
• Added CONTRIBUTING.md and /docs/contribution directory to list detailed steps for contribution
• Updated package.json and package-lock.json and fixed dependencies
• Added search plugin options and updated /docs/.vuepress/config.js
• Added Changelog file

[ravirajsubramanian]

@thakurganeshsinghfw I have reviewed all except src/gen folder contents. Looks good to me.

[kaustavdm]

On a separate note, let's not link to the internal issue tracker. Given this is a public project, we should instead track the issues in the GH issues.

[kaustavdm]

Squashed and merged since there was a merge commit in the branch.