Add a plugin icon which distinguishes it from the upstream global-scoped Secrets Manager credentials provider.

(This should be the Secrets Manager icon, but with a little Jenkins folder icon superimposed on it, in the bottom-right or bottom-left - whichever is the Jenkins UI convention)

It should be possible to exclusively use the folder-scoped Secrets Manager credentials provider, without the global-scoped credentials provider being enabled (or even present).

One way to do this is to split the shared logic out of the regular Secrets Manager provider plugin into a new common plugin. Then have both the global-scope plugin and the folder-scoped plugin depend on it:

aws-secrets-manager-credentials-provider-common
 +-- aws-secrets-manager-credentials-provider-plugin
 +-- aws-secrets-manager-credentials-provider-folders-plugin 

This could be done in a monorepo with a Maven multi-module build. (All projects inside https://github.com/jenkinsci/aws-secrets-manager-credentials-provider-plugin)

It could alternatively be done by putting each one in separate repositories.

The folder-scoped credential provider has a null guard, which is supposed to stop the provider being enabled if it's not configured on a folder.

This works when Jenkins folders are set up with CasC / JobDSL; the folder configuration object will indeed be null.

However, if you create a new folder via the Web UI and set any kind of configuration (for any plugin) on it, the defaults for the folder-scoped credentials provider will get applied automatically when the configuration is saved.

This means it's not possible to configure a folder in the Web UI without also enabling the folder-scoped credentials provider.

We a need a way to stop this happening, so that the folder-scoped credentials provider is only enabled on the folders where the user wants it to be.

Decide whether the folder-scoped credentials provider should support hierarchical config merging.

This is where:

• the folder-scoped provider takes properties X, Y, Z
• a child folder has the folder-scoped provider enabled, but has only set properties X and Y.
• a parent folder has the folder-scoped provider enabled, with property Z set.
• the child uses its own values for X and Y, and inherits property Z from the parent.

(Re-)enable the cache for credentials in the folder-scoped provider, so that it doesn't go to Secrets Manager every time.