[feat] Add support for premium_40GB NodeBalancer type

[komer3]

LinodeGo PR that supports this feature: linode/linodego#867

General:

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Pull Request Guidelines:

1. Does your submission pass tests?
2. Have you added tests?
3. Are you addressing a single feature in this PR?
4. Are your commits atomic, addressing one change per commit?
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6. Have you saved your large formatting changes for a different PR, so we can focus on your work?
7. Have you explained your rationale for why this feature is needed?
8. Have you linked your PR to an open issue

[codecov]

Codecov Report

❌ Patch coverage is 42.85714% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.85%. Comparing base (ed281b9) to head (58457f3).

Files with missing lines	Patch %	Lines
cloud/linode/loadbalancers.go	33.33%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #507      +/-   ##
==========================================
- Coverage   73.72%   70.85%   -2.88%     
==========================================
  Files          19       19              
  Lines        2835     2844       +9     
==========================================
- Hits         2090     2015      -75     
- Misses        504      511       +7     
- Partials      241      318      +77     

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