[plugin-aws-ec2-ebs] add actions to README need to be allowed in the iam policy

[miztch]

I've been setting up mackerel agent with aws-ec2-ebs plugin according to README, and was faced with insufficient AWS IAM policy attachment.

I've recieved two error messages (several ids are masked) and now it turned out that two essential actions (ec2:DescribeInstanceTypes and ec2:DescribeInstances) are not mentioned on README for aws-ec2-ebs plugin. So this PR fixes it.

Aug 28 07:48:10 ip-10-0-0-100 mackerel-agent[409653]: 2024/08/28 07:48:10 INFO <metrics.plugin> command mackerel-plugin-aws-ec2-ebs outputted to STDERR: "2024/08/28 07:48:10 UnauthorizedOperation: You are not authorized to perform this operation. User: arn:aws:sts::123456789012:assumed-role/my-role/i-01234567890abcdef is not authorized to perform: ec2:DescribeInstanceTypes because no identity-based policy allows the ec2:DescribeInstanceTypes action\n\tstatus code: 403, request id: c129b45e-410a-4be8-998c-681a127db319\n"

Aug 28 07:42:00 ip-10-0-0-100 mackerel-agent[408819]: 2024/08/28 07:42:00 INFO <metrics.plugin> command mackerel-plugin-aws-ec2-ebs outputted to STDERR: "2024/08/28 07:42:00 UnauthorizedOperation: You are not authorized to perform this operation. User: arn:aws:sts::123456789012:assumed-role/my-role/i-01234567890abcdef is not authorized to perform: ec2:DescribeInstances because no identity-based policy allows the ec2:DescribeInstances action\n\tstatus code: 403, request id: 99962773-9682-4b1d-922f-79184f2252a5\n"

[yohfee]

Thank you for your contribution!

We fixed CI failure by #1220. Would you mind trying with it?

[miztch]

Thank you, I merged the master branch with the CI fixes into this branch, but the Action did not run.

I'm sorry I don't have idea how to deal with this, is there anything I should do, or is it OK to leave it as it is?

[yohfee]

We are grateful for your assistance!