Document additional limitations/lack thereof for attaching policies

[feorlen]

This access management page notes that JSON policies are limited to 2048 characters.

It should note that there is no limit to the number of policies you may attach to a user or group. Investigate if there are other concerns about attaching a large number of policies (performance?) and include that information as well.

[ravindk89]

https://min.io/docs/minio/linux/reference/minio-mc-admin/mc-admin-policy-create.html#mc.admin.policy.create.POLICYPATH

[ravindk89]

as per engineering:

There's a mistake in the documentation. The policy document size limit is 20KiB

[feorlen]

Also you can't have more than 10 tags. Not directly related to policies, but can be rolled into this change in some appropriate location.