Add Google Analytics, Dotfile, Segment and Square access-review connectors

Two OAuth2 and two API-key connectors:

- Google Analytics (GA4): OAuth2 with both analytics.readonly and
  analytics.manage.users.readonly (readonly alone 403s on the accounts
  list); v1alpha accessBindings enumerated at account and property level
  and merged by email; manual account picker (Pattern 1) with a
  per-connection probe and name resolver; distinct from Google Workspace.
- Dotfile: API key in the X-DOTFILE-API-KEY header (Pattern 3); GET
  /v1/users (owner/admin, suspended_at) with a static probe.
- Segment (Twilio): Public API token as Bearer with a required Region
  setting (US or EU) mapped to the regional host; GET /users plus per-user
  GET /users/{id} for roles and /invites for pending members; per-connection
  BuildProbeURL.
- Square: OAuth2 (EMPLOYEES_READ) or a personal access token (Pattern 3);
  POST /v2/team-members/search returns email/status/is_owner directly, so no
  role resolution; custom probe and name resolver.

Google Analytics and Square are confidential OAuth clients, wired into the
bootstrap OAuth provider list and .env.example. Segment carries a required
extra setting, so the console add-source dialog maps region onto its
segmentRegion API-key input; without that mapping the value is silently
dropped and the create is rejected.

Cassette-backed driver tests plus unit tests for the Segment probe URL and
the bootstrap OAuth provider list.

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

pkg/bootstrap/builder.go

@@ -490,6 +490,8 @@ func (b *Builder) Build() (*probodconfig.FullConfig, error) {
 		"DATADOG",
 		"ZENDESK",
 		"LINEAR",
+		"GOOGLE_ANALYTICS",
+		"SQUARE",
 	} {
 		clientID := b.resolver.getEnv("PROBOD_CONNECTOR_" + provider + "_CLIENT_ID")
 		if clientID == "" {
@@ -614,6 +616,8 @@ func (b *Builder) validateRequired() error {
 		{"CONNECTOR_DATADOG", []string{"CLIENT_SECRET"}},
 		{"CONNECTOR_ZENDESK", []string{"CLIENT_SECRET"}},
 		{"CONNECTOR_LINEAR", []string{"CLIENT_SECRET"}},
+		{"CONNECTOR_GOOGLE_ANALYTICS", []string{"CLIENT_SECRET"}},
+		{"CONNECTOR_SQUARE", []string{"CLIENT_SECRET"}},
 		{"CONNECTOR_VERCEL", []string{"CLIENT_SECRET", "INTEGRATION_SLUG"}},
 	}