Make e2e tests more configurable

[avinal]

Changes

• Add more environment variables to e2e tests to set serverName, serverAddress and certFileName
• Update e2e tests docs with env descriptions
• Fixes #437

/kind misc

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Release Notes

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[tekton-robot]

Hi @avinal. Thanks for your PR.

I'm waiting for a tektoncd member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[enarha]

/ok-to-test

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adambkaplan, sayan-biswas

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