support the aggregate instance-type-base filter

[bwagner5]

Issue #, if available:
N/A

Description of changes:

• Add --base-instance-type as the first aggregate filter
  • Returns similar instance-types based on the instance type passed in to construct flexible fleets if you are already using an instance type.

Example:

$ ec2-instance-selector --base-instance-type t3.large
m1.large
m3.large
m4.large
m5.large
m5a.large
m5ad.large
m5d.large
m5dn.large
m5n.large
t2.large
t3.large
t3a.large

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

Merging #6 into master will increase coverage by 0.21%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
+ Coverage   89.22%   89.44%   +0.21%     
==========================================
  Files           7        7              
  Lines         724      758      +34     
==========================================
+ Hits          646      678      +32     
- Misses         52       53       +1     
- Partials       26       27       +1     

Impacted Files	Coverage Δ
pkg/selector/types.go	100.00% <ø> (ø)
pkg/selector/selector.go	84.07% <88.23%> (+2.04%)	⬆️

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[haugenj]

Very nice ʕ•ᴥ•ʔ

[haugenj]

Are these values derived from somewhere or did you come up with them?

[bwagner5]

They're arbitrary and may be adjusted in the future. I think it's a decent band for an opinionated result set though. It may make sense to adjust the low percentile to 1.0 so that the result set gives instances that are at least as spec'd out as the base.