fix(metastore): make builtin schemas readonly

[greyscaled]

Summary

This adds a restriction in metastore for creating entries on builtin schemas, other than the default schema (public).

Details

Initially, this added a builtin schema glare_uploads (#2614), but we later decided to remove it and instead use a table funcition.
At the time, glare_uploads was chosen because prefixing internal schemas with glare_ reduces collision chance, and is what pg does.

Read more on pg_

From https://www.postgresql.org/docs/current/ddl-schemas.html

Since system table names begin with pg_, it is best to avoid such names to ensure that you won't suffer a conflict if some future version defines a system table named the same as your table. (With the default search path, an unqualified reference to your table name would then be resolved as the system table instead.) System tables will continue to follow the convention of having names beginning with pg_, so that they will not conflict with unqualified user-table names so long as users avoid the pg_ prefix.

Progress

• Add glare_uploads schema
• Make schema read-only
• Add test(s)

[tychoish]

I'm ok with this but @scsmithr or @vrongmeal should give it the once over.

[greyscaled]

I'm ok with this but @scsmithr or @vrongmeal should give it the once over.

sounds good, added them as reviewers.

I've also updated the code since your last review to remove the glare_uploads schema, as we decided to use a table func.