Clarify users with permissions to invite new members to the organisation

[rodolfoBee]

In Sentry UI, it is not 100% clear that users with Member and Admin access don't have permission to directly invite new members to join the organisation. This is clearly documented on this page: https://docs.sentry.io/product/accounts/membership/#admin, where only Managers and Owners are select on Can add/remove/change members.

There are two locations in the UI where this can be improved, see screenshots:

Invite new member page: https://sentry.io/settings/{org}/members/

In this screenshot, it's can be helpful to specify "Only Managers and Owners have permission to invite new members" in addition to the existing text, and/or change "we will send a request to the organisation's Owner and Manager to approve your request".

Role selection page: https://sentry.io/settings/{org}/members/{userID}/

This role description says "they can manage memberships of teams they are members of, " which can lead users to believe admins can invite new members. Adding a note saying does not have permission to directly invite members.

[getsentry-release]

Routing to @getsentry/growth for triage. ⏲️

[imatwawana]

Suggest the following text for Invite New Members UI:
You don't have permission to directly invite users, but we'll send send this request to your organization owner or manager for review.”

Suggest the following text for the Settings > Members UI:
Admin privileges on any teams of which they're a member. They can create new teams and projects, as well as remove teams and projects on which they already hold membership (or all teams, if open membership is enabled). Additionally, they can manage memberships of teams that they are members of. They cannot invite members to the organization.

[priscilawebdev]

Thank you @rbisol @shimizukawa , we'll look at it and see what we can do 😉