rpk: try download plugin directly from cloudsmith

[r-vasquez]

Cover letter

rpk plugin install will try to download the plugin directly from Cloudsmith URL:

https://packages.vectorized.io/cloudv2/raw/names/rpk-plugin-[PLUGIN-NAME]-[OS]-[ARCH]/versions/0.0.3/rpk-plugin-[PLUGIN-NAME]-[OS]-[ARCH]

if an error occurs then it'll fall back to the old behavior of looking for the plugin in the S3 manifest.

Fixes #5785

Backport Required

• [x] v22.2.x

UX changes

• none

Release notes

• none

[ivotron]

i’ve uploaded sample packages to https://cloudsmith.io/~redpanda/repos/rpk-plugins/packages/ . this is an example URL:

https://packages.vectorized.io/rpk-plugins/raw/names/byoc-linux-amd64/versions/0.0.1~alpha1/byoc.tgz

note that the domain will change this week to dl.redpanda.com. so the template will be something like:

https://dl.redpanda.com/rpk-plugins/raw/names/byoc-{{OS}}-{{ARCH}}/versions/{{VERSION}}/byoc.tgz

[ivotron]

fyi, dl.redpanda.com is now active

[r-vasquez]

Closing for now since it's not urgent anymore, please let us know if this is needed, otherwise, we will likely wait for the native cloud top-level command

[ivotron]

reopening as per discussion on reordering priorities for rpk cloudv2 byoc plugin in q3 and q4

[simon0191]

@ivotron @r-vasquez @twmb Are we ok with hardcoding an entitlement token in a public repo? Is the scope of the token limited to rpk plugins repo? Why not making that repo public?

[ivotron]

the repo has been made public

[r-vasquez]

Thanks @ivotron, changed the code to use the public URL:

https://dl.redpanda.com/rpk-plugins/raw/names/byoc-linux-amd64/versions/0.0.1~alpha1/byoc.tgz