Add Bitbucket installation type option (#3999)

The Bitbucket source has some logic to autodetect whether it's talking to Bitbucket Cloud or something self-hosted, but we have encountered a situation in which it looks like this logic is causing problems. This new option will be used to disable that functionality to confirm this hypothesis.

pkg/pb/sourcespb/sources.pb.validate.go

@@ -658,6 +658,8 @@ func (m *Bitbucket) validate(all bool) error {
 
 	// no validation rules for SkipArchives
 
+	// no validation rules for InstallationType
+
 	switch v := m.Credential.(type) {
 	case *Bitbucket_Token:
 		if v == nil {

proto/sources.proto

@@ -92,6 +92,12 @@ message AzureStorage {
   repeated string storage_containers = 5;
 }
 
+enum BitbucketInstallationType {
+  AUTODETECT = 0;
+  CLOUD = 1;
+  DATA_CENTER = 2;
+}
+
 message Bitbucket {
   string endpoint = 1 [(validate.rules).string.uri_ref = true];
   oneof credential {
@@ -104,6 +110,7 @@ message Bitbucket {
   repeated string ignore_repos = 6;
   bool skip_binaries = 7;
   bool skip_archives = 8;
+  BitbucketInstallationType installation_type = 9;
 }
 
 message CircleCI {