Add Jira proxy settings columns

What does this MR do?

In order to configure the Jira proxy settings, we need to store the following values:

• proxy_address
• proxy_port
• proxy_username
• proxy_password

This creates the database columns in the jira_tracker_data table.

Migration script

rails db:migrate

$ rails db:migrate
== 20210119153801 AddProxySettingsToJiraTrackerData: migrating ================
-- add_column(:jira_tracker_data, :encrypted_proxy_address, :text)
   -> 0.0020s
-- add_column(:jira_tracker_data, :encrypted_proxy_address_iv, :text)
   -> 0.0005s
-- add_column(:jira_tracker_data, :encrypted_proxy_port, :text)
   -> 0.0004s
-- add_column(:jira_tracker_data, :encrypted_proxy_port_iv, :text)
   -> 0.0003s
-- add_column(:jira_tracker_data, :encrypted_proxy_username, :text)
   -> 0.0003s
-- add_column(:jira_tracker_data, :encrypted_proxy_username_iv, :text)
   -> 0.0003s
-- add_column(:jira_tracker_data, :encrypted_proxy_password, :text)
   -> 0.0003s
-- add_column(:jira_tracker_data, :encrypted_proxy_password_iv, :text)
   -> 0.0003s
== 20210119153801 AddProxySettingsToJiraTrackerData: migrated (0.0047s) =======

rails db:migrate:down VERSION=20210119153801

$ rails db:migrate:down VERSION=20210119153801
== 20210119153801 AddProxySettingsToJiraTrackerData: reverting ================
-- remove_column(:jira_tracker_data, :encrypted_proxy_password_iv, :text)
   -> 0.0013s
-- remove_column(:jira_tracker_data, :encrypted_proxy_password, :text)
   -> 0.0003s
-- remove_column(:jira_tracker_data, :encrypted_proxy_username_iv, :text)
   -> 0.0003s
-- remove_column(:jira_tracker_data, :encrypted_proxy_username, :text)
   -> 0.0003s
-- remove_column(:jira_tracker_data, :encrypted_proxy_port_iv, :text)
   -> 0.0003s
-- remove_column(:jira_tracker_data, :encrypted_proxy_port, :text)
   -> 0.0003s
-- remove_column(:jira_tracker_data, :encrypted_proxy_address_iv, :text)
   -> 0.0004s
-- remove_column(:jira_tracker_data, :encrypted_proxy_address, :text)
   -> 0.0003s
== 20210119153801 AddProxySettingsToJiraTrackerData: reverted (0.0068s) =======

Related to #216912 (closed)