[improvement] Add NetworkHelper field to LinodeMachineSpec and update instance configuration logic

[komer3]

• Introduced a new optional boolean field NetworkHelper in LinodeMachineSpec to indicate if the network helper should be used, defaulting to true.
• Updated the instance configuration logic in linodemachine_controller.go to enable the network helper based on the new field.

Note: Disabled for flatcar based flavor (set to false)

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

[codecov]

Codecov Report

Attention: Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 63.16%. Comparing base (eb218ad) to head (a10de84).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/controller/linodemachine_controller.go	85.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #806      +/-   ##
==========================================
- Coverage   63.16%   63.16%   -0.01%     
==========================================
  Files          71       71              
  Lines        7292     7305      +13     
==========================================
+ Hits         4606     4614       +8     
- Misses       2415     2419       +4     
- Partials      271      272       +1     

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