Calculate cpu and mem savings in tortoise

[randytqwjp]

What this PR does / why we need it:

Calculates CPU and MEM savings based on min/max replica changes.

Which issue(s) this PR fixes:

#411

Fixes #

Special notes for your reviewer:

[randytqwjp]

Also, you must be careful about the fact that changing metrics is a breaking change that we must avoid. If you think you might have to change the metrics in the future, make sure you mention that in the metric description (i.e. Help), like Help: "..... This metric is the alpha stage and can be breaking-changed in the future releases."

Especially since you released v1 recently, we need to be careful about the breaking change, in general.

i did not know this. I will make the changes

[randytqwjp]

@sanposhiho For release version, does this mean we have to release v2 in this case? because there are some changes to the metrics

[sanposhiho]

Let's just go ahead with v1.1.0 in this case; releasing v2 just for those metrics is too much for us. I just wanted to prevent the same thing from happening again in the future. (Although as you said if we followed the compatibility strictly, releasing v2 would be the most suitable option. So, just keep it in mind as your learning, there're many projects, especially in OSS world, which follow the semantic versioning very strictly)

Please mention this change at a release note when you release v1.1.0. That would help users (including us) to see what breaking changes are introduced in which version. (of course, we should try to avoid a breaking change as much as possible in the first place though) Also, like I said earlier, let's make sure we have a clear note on each metric in the future, if the metric could be breaking-changed later.

[randytqwjp]

@sanposhiho made the changes PTAL