[Improvement] remove the restriction for custom policy type

[FANNG1]

What would you like to be improved?

We could only create one custom policy type

How should we improve?

remove the restriction for custom policy type to support more type like custom-ttl, custom-compaction

[FANNG1]

cc @mchades

[mchades]

Can you describe the use case? Why can't it be solved through the policy name? I think we should add more built-in types instead of supporting custom type names.

[FANNG1]

Built-in types couldn't cover all policies. Suppose there is a custom compact policyA with parameterA, compact policyB with parameterB, the other components will do same action according to the policy type like get small file stats, submit compact jobs.