Allow underscore in tenant names

Overview

Presently, tenant names are restricted to the following pattern: [a-z][a-z0-9]{0,30}.  This is too restrictive for naming conventions used by FSE.  

There are naming restrictions in Keycloak and Postgres.  The restriction in the manager components need to take both of these into consideration

• Keycloak:  The Realm name must not contain spaces, or any special character other than "_" or "-".

• Postgres:   _ is allowed, - and spaces are not.  Length must be < 64 bytes

Approach

Adjust the naming convention to allow underscores in tenant names, as these are allowed in both Keycloak and Postresql.  With this, FSE can continue to use existing naming conventions.

• Old Pattern:  [a-z][a-z0-9]{0,30}

• New Pattern:  [a-z][a-z0-9_]{0,29}[a-z0-9]

Acceptance Criteria

• mgr-tenants allows tenant names adhering to the new pattern above

• tests have been updated

• a demonstration has been given to the team

Additional Info/Links

See https://folio-org.atlassian.net/wiki/display/TC/DR-000002+-+Tenant+Id+and+Module+Name+Restrictions.  In pages linked from here, a potential name clash is described, but it seems highly unlikely to happen unless tenants use suffixes like _mod or _edge and modules which don't use the standard mod- or edge- name prefix.  If needed, we can consider adding checks for these to mgr-tenants to prevent this from happening.