[COST-5432] - Add the ability to generate reserved instances

[lcouzens]

Small EC2 generator update to add the ability to gen Reserved instances.

Testing:
nise -lll report aws --aws-s3-bucket-name ~/location_to_gen_files_in/ --aws-s3-report-name my_report --static-report-file ~/location/yaml_file.yml

Yaml example:

generators:
  - EC2Generator:
      start_date: last_month
      processor_arch: 64-bit
      resource_id: 55555555
      product_sku: VEAJHRNKTJZQ
      region: us-east-1a
      instance_type:
        inst_type: m5.large
        physical_cores: 1
        vcpu: 2
        memory: '8 GiB'
        storage: 'EBS Only'
        family: 'General Purpose'
        reserved_instance: True
  


accounts:
  payer: 9999999999998
  user:
    - 9999999999998

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.7%. Comparing base (48cbacc) to head (7d9196a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #538   +/-   ##
=====================================
  Coverage   93.7%   93.7%           
=====================================
  Files         62      62           
  Lines       4646    4657   +11     
  Branches     644     645    +1     
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+ Hits        4351    4362   +11     
  Misses       158     158           
  Partials     137     137