verify subcommand should use ssm:GetParameters to simulate actual ECS' behavior

[aereal]

Expected behavior

ecspresso verify with the IAM role that allowed only ssm:GetParameters action should successfully get the parameter(s) from AWS Systems Manager Parameters Store.

Actual behavior

It fails due to lack of the permission to call ssm:GetParameter (the singular one, not the plural one).

refs.

ecspresso/verify.go

Line 119 in ec85dec

_, err := v.ssm.GetParameter(ctx, &ssm.GetParameterInput{

Proposed solution

It calls ssm:GetParameters instead of ssm:GetParameter.

That change also introduce the chance to reduce the API calls.

[fujiwara]

@aereal Thank you! v2.3.3 released!
https://github.com/kayac/ecspresso/releases/tag/v2.3.3

I added #681 for backward compatibility. When GetParameters API fails with "access denied", fallback to GetParameter API with warning logs. This fallback will be removed v2.4.