examples: multi-tenant seed script, readme and other improvements

[bratvanov]

Seed script

1. Fix duplicate username for the [email protected] user (changed username from user3 to multi-admin, as user3 already exists for the [email protected] email address).
2. Unify all users to use the demo password instead of test, as is the convention with all other Payload examples.
3. Change the example tenant domains from localhost.com (which is privately registered) to the .test TLD, recommended as per rfc2606 for testing.

Readme

1. Document the tenant users (previously, it was difficult to find the usernames/passwords without looking at the seed script)
2. Add a command to copy the example environment variables
3. Fix the provided hosts file code to be on a single line, removed the ports (which don't work in hosts files), and added 127.0.0.1.
4. Minor grammar changes

package.json

• Removed the local file file:payloadcms-plugin-multi-tenant-3.15.1.tgz from the dependencies, instead we fetch the latest version - fixes examples/multi-tenant references "@payloadcms/plugin-multi-tenant": "file:payloadcms-plugin-multi-tenant-3.15.1.tgz", #10602

Other

• Fixed typo in exported access const superAdminOrTeanantAdminAccess -> superAdminOrTenantAdminAccess

[bratvanov]

👋 Hey @JarrodMFlesch do you mind reviewing this, and letting me know if it looks good? Thanks!

[JarrodMFlesch]

Thanks for this and thanks for pinging me! Looked good, merged 👍

[github-actions]

🚀 This is included in version v3.21.0