Add Linear integration support

[sergeibbb]

Description

Fixes #3991

• Related GKDev issue: Support Linear as an issue tracker in our JS provider library
  • and the library: GKDEV-2730-linear-prototype-for-gitlens
  • and related Slack conversation
• We need to add full support for all functionality that we have for Jira in order to do so.
• Linear's SDK
• Consider while using Linear SDK:
  • It's always nice if an SDK allows a method of overriding how network requests are made.
  • proper tree shaking