Added ability to override LATTICE_ENDPOINT env variable with helm

[xWink]

What type of PR is this?

feature

Which issue does this PR fix:
N/A

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

• Adds ability to override VPC Lattice endpoint when using helm

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

Testing done on this change:

N/A

Automation added to e2e:

N/A

Will this PR introduce any new dependencies?:

No

Will this break upgrades or downgrades. Has updating a running cluster been tested?:
No

Does this PR introduce any user-facing change?:

No

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

[coveralls]

Pull Request Test Coverage Report for Build 6617925452

• 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 45.363%

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Totals
Change from base Build 6569460474:	0.0%
Covered Lines:	4026
Relevant Lines:	8875

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💛 - Coveralls