feat: determine cluster ID from cluster name (label) if in LKE mode

[AshleyDumaine]

At startup when creating the operator, if in LKE mode (default) we automatically determine the cluster ID from the name and fail if there is not one match returned.
Other providers take a cluster name rather than an ID if using managed K8s, so this is to follow the standard convention.

Also adding a GHA change to make sure we build and push images for main so the latest tag exists for linode/karpenter-provider-linode so the README steps work without needing to build and push the image first + update the deployment image.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.99%. Comparing base (3f03a8a) to head (c7e7cf0).

Files with missing lines	Patch %	Lines
pkg/operator/operator.go	0.00%	14 Missing ⚠️
pkg/fake/linodeapi.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
- Coverage   67.37%   66.99%   -0.38%     
==========================================
  Files          37       37              
  Lines        2296     2306      +10     
==========================================
- Hits         1547     1545       -2     
- Misses        599      612      +13     
+ Partials      150      149       -1     

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