Change labels and help text for invite members modal [RUN ALL RSPEC]

What does this MR do?

Resolves Technical Writing review of all labels and help text in Invite Members modal https://gitlab.com/gitlab-org/gitlab/-/issues/301014

Related to feature flag rollout issue https://gitlab.com/gitlab-org/gitlab/-/issues/247208

Changes:

• Modal title: Invite members (Change from "Invite team members")
• Field label: GitLab member or email address (Change from "GitLab member or Email address")
• Field help text: Select members or type email addresses (Change from "Search for members to invite")

Screenshots (strongly suggested)

before	after

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #301014