Add Support For btree_gist Extension

[logston]

Is your feature request related to a problem? Please describe.
It would be great to have support for the btree_gist extension.

Describe the solution you'd like
Ability to enable the same behavior that is available in PostgreSQL under the extension of the same name.

Describe alternatives you've considered
None at the moment. I'm simply showing interest in having this feature available.

Additional context

postgres=# CREATE EXTENSION IF NOT EXISTS btree_gist;
ERROR:  at or near "EOF": syntax error: unimplemented: this syntax
DETAIL:  source SQL:
CREATE EXTENSION IF NOT EXISTS btree_gist
                                        ^
HINT:  You have attempted to use a feature that is not yet implemented.

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Jira issue: CRDB-3992

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[kahuang]

This would be useful in combination with *_range datatype support, where you can use this index to prevent range overlaps

[giangpham712]

@fqazi this issue affects efcore.pg tests