RFE: modify `cosa buildfetch` to support OCP versions

Feature Request

I'd like to be able to specify an OCP version when doing cosa buildfetch so that I can see a more accurate representation of changes when doing a new RHCOS build.

Desired Feature

Ultimately, I want to be able to accurately report the different RHSAs that are included in an RHCOS build when compared to the last z-stream release for an OCP version.

Example Usage

$ cosa buildfetch --ocp 4.10
Fetching update graph for OCP stable-4.10 stream...
Found latest OCP 4.10.z release: 4.10.14
Found RHCOS 410.84.202205131801-0
Updated builds/builds.json
Fetching: s3://art-rhcos-ci/releases/rhcos-4.10/410.84.202205131801-0/x86_64/meta.json
Fetching: s3://art-rhcos-ci/releases/rhcos-4.10/410.84.202205131801-0/x86_64/commitmeta.json
Fetching: s3://art-rhcos-ci/releases/rhcos-4.10/410.84.202205131801-0/x86_64/ostree-commit-object

Other Information

Could potentially provide another flag to select the OCP channel (eus, fast, stable)

$ cosa buildfetch --ocp 4.10 --channel fast
Fetching update graph for OCP fast-4.10 stream...
Found latest OCP 4.10.z release: 4.10.14
Found RHCOS 410.84.202205131801-0
Updated builds/builds.json
Fetching: s3://art-rhcos-ci/releases/rhcos-4.10/410.84.202205131801-0/x86_64/meta.json
Fetching: s3://art-rhcos-ci/releases/rhcos-4.10/410.84.202205131801-0/x86_64/commitmeta.json
Fetching: s3://art-rhcos-ci/releases/rhcos-4.10/410.84.202205131801-0/x86_64/ostree-commit-object

Start at the cosa buildfetch command and compare its current behavior with the example invocation in the issue. Trace how it selects the update graph and RHCOS build, then verify that an OCP version produces the corresponding build data and that the optional channel behavior is defined.