Rename env to EC2_INSTANCE_TAG

[jongwooo]

Proposed changes:

Related issue litmuschaos/litmus#4807 (comment)

This PR fixes an issue where the ec2-stop-by-tag experiment fails to target the intended EC2 instance.

The ec2-stop-by-tag experiment encounters a TARGET_SELECTION_ERROR due to an incorrect retrieval of the EC2_INSTANCE_TAG environment variable.

Fault Summary:
TARGET_SELECTION_ERROR
{"errorCode":"TARGET_SELECTION_ERROR","phase":"PreChaos","reason":"failed to get the instance tag, invalid instance tag","target":"{EC2 Instance Tag: , Region: ap-northeast-2}"}

By correctly renaming the environment variable from INSTANCE_TAG to EC2_INSTANCE_TAG, we can accurately target the intended EC2 instance.

Special notes for your reviewer:

cc. @namkyu1999

Checklist:

• Fixes #
• PR messages has document related information
• Labelled this PR & related issue with breaking-changes tag
• PR messages has breaking changes related information
• Labelled this PR & related issue with requires-upgrade tag
• PR messages has upgrade related information
• Commit has unit tests
• Commit has integration tests
• E2E run Required for the changes

[ispeakc0de]

Can you fix the pre-checks build?

The following files were found to be not go formatted:
pkg/kube-aws/ec2-terminate-by-tag/types/types.g

[Jonsy13]

Hi @jongwooo
Can you please fix the failing check in this PR, it should be fixed by running gofmt.
Command - gofmt -w .

[jongwooo]

@Jonsy13 Sure thing:)