refactor: move bootstrap sequence into dedicated bootstrap.go

[Aditya-132]

Proposed changes

Refactors the bootstrap logic in the secure agent into its own file for
better separation of concerns:

• Extract performBootstrapSequence and its helper functions
  (discoverBootstrapURLs, doHandleBootstrapRedirect,
  doRequestBootstrapServerOnboardingInfo, etc.) out of daemon.go
  into a new bootstrap.go. daemon.go now only holds RunCommandDaemon.
• Move the corresponding unit tests from daemon_test.go into a new
  bootstrap_test.go.
• Fix the RunCommand and DaemonCommand tests by setting the status
  file paths (StatusFilePath, ResultFilePath, SymLinkDir) so
  prepareStatus can create its directory instead of failing on an
  empty path (mkdir "": no such file or directory).

Closes #455

Types of changes

• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices applies)

Checklist

• I have signed the comm
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if
  appropriate)
• I have added necessary documentation (if appropriate)

Dependency

• None.

Special notes for your re

This is primarily a code-organization refactor with no behavior change to
the bootstrap flow. The only functional change is in the test setup: the
existing RunCommand/Daemobecause prepareStatus(added with the status command) needs valid status paths; they now uset.TempDir()` so the suite runs green.

[Aditya-132]

@glimchb