[Feature]: Improve validation of org name and slug

[SuaYoo]

Applicable to org settings and org rename step following https://github.com/webrecorder/browsertrix/pull/1870.

Changes

• [x] Differentiate between org name and slug field errors - see Ilya's comment on mongo DuplicateKeyError: https://github.com/webrecorder/browsertrix/pull/1891#issuecomment-2192240438
• [ ] Show org name and slug min/max help text consistently
• [ ] Check org slug on blur with GET /orgs/slug-lookup

Original context:

Once https://github.com/webrecorder/browsertrix/pull/1891 is merged, we can also check for an invalid slug, which will return the detail invalid_slug.

If we want to check that an org slug is not a duplicate of an existing one ahead of time, we also have the GET /orgs/slugs and GET /orgs/slug-lookup endpoints available already in the API.

_Originally posted by @tw4l in https://github.com/webrecorder/browsertrix/pull/1870#discussion_r1655185460_

[tw4l]

Ah, realized /orgs/slug-lookup is superuser only, so that might not actually work. Maybe better to check on submission after all.

[tw4l]

PR opened to return and handle duplicate_org_name and duplicate_org_slug - further improvements to be made in separate PRs.