feat: efficient journey bundling and hashing

[vigneshshanmugam]

• fix fix: update hash logic to account for bundling #804 correctly
• The previous solution of updating the bundle hash based on the file contents is problematic due to the following reasons
  • The bundle would contain both journeys because they are in same file
  • If one of the journey imports big external lib, it affects the size of others as well.
  • The more external deps, the bigger the problem and every change would indirectly affect the Kibana SO updates.
• The proposed solution addresses the problem by adding a pre-transform phase where we help the bundler (esbuild) to do better DCE (Dead Code elimination) on individual journey functions as bundlers work on file level entries not lower levels.