Enable join between pr_history and issues table #181

Metrics to track;

• Average turnaround time of different tickets (cut by org name, Tech stack, ticket type etc)
• Low engagement tickets ie multiple PRs raised but ticket not closed
• Average PRs per Ticket

For this we need to join issues and pr_history table. Earlier, ccbp_tickets and pr tables were matched on ticket_url but ticket_url of pr table does not store the ticket link but the api links resulting in no way to match the 2 tables.

Objective : To enable join between the 2 tables either by adding ticket_link column in pr_history table or add issueID in the same.