Kibana should tell the user she can't create a space with already existing name instead of just error

[bhavyarm]

Kibana version: 7.5.2 BC1

Elasticsearch version: 7.5.2 BC1

Server OS version: darwin_x86_64

Browser version: chrome latest

Browser OS version: os x

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: Kibana displays "Error saving space:" when user tries to create a space with existing space name.

Kibana should tell the user - space name needs to be modified.

Steps to reproduce:

1. Create a space_a
2. Try to create space_a again
3. Kibana displays Error saving space

Screenshots (if relevant):

Errors in browser console (if relevant):

Failed to load resource: the server responded with a status of 409 (Conflict)

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)

[marius-dr]

Same in 7.6.0. A few more details on it:

• the error comes from the URL identifier as that has to be unique.
• if you change the identifier with the "Customize" option, you can have spaces with the same name.

[jportner]

This was fixed in 7.7 and 8.0 when the Spaces client was migrated to the New Platform (#54298):

Reference