Fix: customize demo cluster port

[vincent0426]

Tracking issue

Closes #3792

Why are the changes needed?

• As stated in [Flytectl Feature] flytectl demo cluster - configurable port number #3792, when a developer uses Docker Desktop with Kubernetes running on port 6443, they must shut it down before running the demo cluster

• Allow users to configure the demo cluster port if needed

What changes were proposed in this pull request?

1. Add a new parameter port, e.g., flytectl demo start --port 6443
2. Dynamically retrieve k8sEndpoint from sandbox_config.go instead of using fixed ones
3. Refactor reload.go to retrieve sandbox config (follow other file structure under flyte/flytectl/cmd/demo)

How was this patch tested?

Tested that parameters were automatically generated with make generate

Setup process

1. Run a k8s cluster that uses port 6443 (docker desktop k8s for testing)
2. Start the demo cluster without specifying port, which defaults to :6443 (expected to fail)
3. Start the demo cluster with port 6444
4. kubectl --server=https://localhost:6444 get pods
5. export FLYTECTL_CONFIG= ~/<pathTo>/.flyte/config-sandbox.yaml
6. Run the test with any pyflyte run --remote

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Docs link

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[eapolinario]

Can you also modify the creation of the kubeconfig file to point to this new port? Trace uses of https://github.com/flyteorg/flyte/blob/master/flytectl/pkg/docker/docker_util.go#L31

As part of initializing the sandbox we write a kubeconfig file that simplifies access to the cluster. That kubeconfig file lives under ~/.flyte/sandbox/.

[codecov]

Codecov Report

Attention: Patch coverage is 24.39024% with 31 lines in your changes missing coverage. Please review.

Project coverage is 36.85%. Comparing base (9486172) to head (3048b00).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
flytectl/pkg/sandbox/reload.go	0.00%	26 Missing ⚠️
flytectl/pkg/sandbox/start.go	25.00%	3 Missing ⚠️
...tl/cmd/config/subcommand/sandbox/sandbox_config.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5969      +/-   ##
==========================================
- Coverage   36.86%   36.85%   -0.01%     
==========================================
  Files        1310     1312       +2     
  Lines      131246   131251       +5     
==========================================
- Hits        48380    48372       -8     
- Misses      78668    78684      +16     
+ Partials     4198     4195       -3     

Flag	Coverage Δ
unittests-datacatalog	51.58% <ø> (ø)
unittests-flyteadmin	54.05% <ø> (ø)
unittests-flytecopilot	11.73% <ø> (ø)
unittests-flytectl	62.26% <24.39%> (-0.13%)	⬇️
unittests-flyteidl	6.92% <ø> (ø)
unittests-flyteplugins	53.84% <ø> (ø)
unittests-flytepropeller	42.90% <ø> (ø)
unittests-flytestdlib	55.42% <ø> (ø)

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