Plugins: Add more filtering capabilities to list() method

[amotl]

@bhks pointed us to corresponding code, where all the possible filtering parameters are enumerated. Thanks. The library may support them in the future.

https://github.com/grafana/grafana/blob/main/pkg/api/plugins.go#L48

Originally posted by @amotl in #115 (comment)

[amotl]

Dear @bhks,

@bhks: May we humbly ask you if you have a need for this, and how strong it is? ;]

With kind regards,
Andreas.