Add API to get domain

[zychen5186]

Why are the changes needed?

1. While integrating interactive CLI into flytectl, I would need to allow users to select the domain for the project in commands like flytectl get execution.

What changes were proposed in this pull request?

1. Add GetDomains API in flyteidl
2. Server GetDomains implementation in flyteadmin,
3. Client GetDomains implementation in flytectl

How was this patch tested?

Tested by running flyteadmin with dev cluster and called the GetDomains function in AdminFetcherExtClient by flytectl.

Added unit test to:

1. flyte/flyteadmin/tests/project_test.go
2. flyte/flytectl/pkg/ext/domain_fetcher_test.go

Setup process

flytectl demo start --dev
POD_NAMESPACE=flyte ./flyte start --config flyte-single-binary-local.yaml

Screenshots

Check all the applicable boxes

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

Related PRs

In order to support domain selection in interactive CLI

Docs link

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 12 lines in your changes missing coverage. Please review.

Project coverage is 60.98%. Comparing base (59e18d1) to head (95f2bca).
Report is 1 commits behind head on master.

Files	Patch %	Lines
flyteadmin/pkg/rpc/adminservice/project.go	0.00%	10 Missing ⚠️
flytectl/pkg/ext/domain_fetcher.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5443   +/-   ##
=======================================
  Coverage   60.97%   60.98%           
=======================================
  Files         793      794    +1     
  Lines       51350    51370   +20     
=======================================
+ Hits        31312    31326   +14     
- Misses      17152    17157    +5     
- Partials     2886     2887    +1     

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.68% <60.00%> (+0.01%)	⬆️
unittests-flytecopilot	17.79% <ø> (ø)
unittests-flytectl	67.96% <60.00%> (-0.01%)	⬇️
unittests-flyteidl	79.04% <ø> (ø)
unittests-flyteplugins	61.84% <ø> (ø)
unittests-flytepropeller	57.30% <ø> (ø)
unittests-flytestdlib	65.80% <ø> (ø)

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[pingsutw]

Thank you, some minor comments

[pingsutw]

LGTM, thank you!