Add ability to pass CLUSTER_NAME env variable in helm chart

[zijun726911]

What type of PR is this? Fix #435

Referred that PR #264

Which issue does this PR fix:

What does this PR do / Why do we need it:

If an issue # is not available please add repro steps and logs from aws-gateway-controller showing the issue:

Testing done on this change:

Automation added to e2e:

Will this PR introduce any new dependencies?:

Will this break upgrades or downgrades. Has updating a running cluster been tested?:

Does this PR introduce any user-facing change?:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

Pull Request Test Coverage Report for Build 6513732297

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 45.361%

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Totals
Change from base Build 6513019827:	0.0%
Covered Lines:	3950
Relevant Lines:	8708

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 6513795831

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 45.361%

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Totals
Change from base Build 6513019827:	0.0%
Covered Lines:	3950
Relevant Lines:	8708

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💛 - Coveralls

[solmonk]

Thanks for working on this, but I think we should not close the referring issue until proper documentation is delivered.