Add Better Stack access review connector

Better Stack exposes team members and pending invitations through its
Uptime API. Wire it as an access-review connector so a Better Stack
team can be reviewed in access-review campaigns.

Better Stack has no third-party OAuth app for listing members (its
OAuth is an end-user MCP sign-in), so the connector authenticates with
a Bearer API token plus the team name that scopes the team-members
listing. The driver paginates /api/v2/team-members, maps roles and
invitation records into account records, and the source name is
resolved from the configured team.

This wires the full surface: the provider enum and migration, the
connector settings, the registry registration with the team-name extra
setting, the GraphQL input and resolver marshaling, the frontend field
mapping and connector logo, and cassette-backed driver tests.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/coredata/connector_settings.go

@@ -136,6 +136,10 @@ type (
 	ZendeskConnectorSettings struct {
 		Subdomain string `json:"subdomain"`
 	}
+
+	BetterStackConnectorSettings struct {
+		TeamName string `json:"team_name"`
+	}
 )
 
 // GrantType returns the OAuth2 grant type recorded on the connector's