Document how cloud scanner provides estimations for Block storage (EBS)

[demeringo]

Bug description

Cloud scanner can provide estimations about impacts of Block Storage but this is not clearly explained in the doc.

In particular:

• supported volume types:
  • St1 and sc1 => approximated as HDD
  • gp2 and gp3 => approximated as SSD
• explicit that we return only manufacture impact (no data for the use phase in API)
• explicit if we return all volumes (attached or not to an instance)

To Reproduce

Expected behavior

Add a chapter in the documentation to explain how EBS impacts are estimated depending on the type of storage.

JSON OUTPUT

Additional context

• Storage types:

  cloud-scanner/cloud-scanner-cli/src/model.rs

  Line 114 in 7f27a7c

  BlockStorage {

• How different storage types are approximated:

  cloud-scanner/cloud-scanner-cli/src/boavizta_api_v1.rs

  Line 94 in 7f27a7c

  match storage_type.as_str() {

[demeringo]

See also the exchanges in Boavizta Public chat: https://chat.boavizta.org/public-boavizta/pl/1h9hnk3h638axqffcqeyjf69dw

[demeringo]

In Cloud Scanner, today EBS volumes are (very roughly!) approximated by either SSD or HDD (from the Boavizta API) depending on the AWS storage type.

Basically,

EBS volumes of type "st1" or "sc1" are approximated as HDD.
EBS volumes of types gp2 and gp3 are approximated as SSD.