Fixes some wordings around system index permission access and usage

[DarshitChanpura]

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[cwillum]

@DarshitChanpura Thanks for the thorough review. I now see the configuration is a little different than I'd understood it before. So I've made some suggestions.

[cwillum]

The fictional name was meant to be an abbreviation for "alerting-maintenance-role". But that's fine. Why not call it simply "alerting-role"?

[DarshitChanpura]

even better. my understanding was it might have been a typo.

[cwillum]

Good call on renaming this.

[cwillum]

This is a new consideration that I hadn't covered before. So I've rewritten this section.

Suggested change

	System index permissions are specified under `index_permissions` in the `roles.yml` configuration file (See [roles.yml]({{site.url}}{{site.baseurl}}/security/configuration/yaml/#rolesyml).) and can be granted permission to as any regular index by specifying the action `system:admin/system_index` under `allowed_actions`. Here is an example, the `.opendistro-alerting-config` system index stores configurations for the Alerting plugin.
	System index permissions are specified under `index_permissions` in the `roles.yml` configuration file (See [roles.yml]({{site.url}}{{site.baseurl}}/security/configuration/yaml/#rolesyml).) along with standard index permissions. They are, however, distinguished from standard index permissions in two ways. A system index permission name begins with the prefix `.opendistro`, and it is defined under `allowed_actions` as `system:admin/system_index`.
	For example, the system index permission that gives a user permission to modify the system index that stores configurations for the Alerting plugin is defined by the index pattern `.opendistro-alerting-config` and its allowed action is defined as `system:admin/system_index`. The following role shows how this system index permission is configured along with other attributes:

[DarshitChanpura]

I don't think the system index permissions always begin with .opendistro, i know they begin with . but that is more of a convention than a constraint.

[cwillum]

Suggested change

	When set to `true`, the feature is enabled and users with access to modify roles can add the `system:admin/system_index` as an allowed action and an index pattern in the roles that will be used for system index access.
	When set to `true`, the feature is enabled and users with access to modify roles can add an index pattern and action for a system index permission to a role.

[DarshitChanpura]

made a slight tweak here. '... and the allowed action system:admin/system_index to a role.'

[cwillum]

Suggested change

	To learn more about system index permissions, see [System Index permissions]({{site.url}}{{site.baseurl}}/security/access-control/permissions/#system-index-permissions) in Permissions documentation.
	To learn more about system index permissions, see [System index permissions]({{site.url}}{{site.baseurl}}/security/access-control/permissions/#system-index-permissions) in Permissions documentation.

[cwillum]

Suggested change

	## System Index permissions
	## System index permissions

[DarshitChanpura]

@cwillum Addressed all the comments. please have another lookeru.

[cwillum]

Just one last suggestion.

[cwillum]

Suggested change

Along with standard index permissions, system index permissions are specified in the 'roles.yml' configuration file under 'index_permissions' (See [roles.yml](site.urlsite.baseurl/security/configuration/yaml/#rolesyml). The user gains access to the system index by specifying `system:admin/system_index` in the role's `allowed_actions` section. With the addition of this action, all system indices covered by patterns defined in `index_patterns` are now accessible to this role. The `*` pattern, on the other hand by itself, is an exception that cannot be used to grant access to all system indices at once.

Along with standard index permissions, you specify system index permissions in the 'roles.yml' configuration file under 'index_permissions' (See [roles.yml](site.urlsite.baseurl/security/configuration/yaml/#rolesyml). You do this by specifying `system:admin/system_index` in the role's `allowed_actions` section and adding the system index in the `index_patterns` section.

"The * pattern, on the other hand by itself, is an exception that cannot be used to grant access to all system indices at once." is already stated below this in the "following considerations" bullet points. Let's say this here or there, but not both places.

[DarshitChanpura]

aah, good catch, i will use your suggestion here.