Promote new Planner member role in product
### Summary
We are launching a new planner role (https://gitlab.com/gitlab-org/gitlab/-/issues/482733) and want to inform users of this addition, so they can leverage it for existing roles or when adding new users to Groups/Projects.
### Proposal
**Add a temporary promotion for the Planner role addition.**
- Disable the promotion in %18.2
- After this is disabled, we should remove the corresponding code.
#### 1. Add a banner to the `Group/Project Members` page and the `Roles and permissions` page in Group settings (Text to be confirmed)
##### Text
`The Planner role is a hybrid of the existing Guest and Reporter roles but designed for users who need access to planning workflows. For more information about the new role, see [our blog](URL) or [learn more about roles and permissions](URL).`
**Illustration SVG:** [`add-user-sm.svg`](https://gitlab-org.gitlab.io/gitlab-svgs/illustrations?q=illustrations%2Fadd-user-sm.svg)

#### 2. Add a contextual promotion to the `Group/Project Members` page invite form (badge + popover)
<mark>:exclamation: **This is subject to low level of effort – please provide estimation**</mark>
##### Text
`The Planner role is a hybrid of the existing Guest and Reporter roles but designed for users who need access to planning workflows. [Learn more about roles and permissions](URL).`
<kbd></kbd>
[View dropdown code location here](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/invite_members/components/invite_modal_base.vue#L310)
### Design resources
- :mag: [View in Figma](https://www.figma.com/design/NCOLgJm9n4X9ajZSATR6cD/Planner-Role?node-id=6-1795&t=YQPT3g36XE9s7a20-1)
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