AWS::Serverless::Api Tags are not visible in the API Gateway console under "Configure Tags"

**Description:**

**Steps to reproduce the issue:**
1. Prepare a SAM template with tags configured for API, eg:

"ApiGatewayRestApi": {
"Properties": {
"Name": "Inbox",
"Tags": [
{
"Key": "custom:stack-name",
"Value": {
"Ref": "AWS::StackName"
}
},
{
"Key": "custom:resource-name",
"Value": {
"Fn::Sub": "${AWS::StackName}-ApiGatewayRestApi"
}
}
]
},
"Type": "AWS::Serverless::Api"
}
2. Use aws cloudfromation package and then deploy to deploy the template
3. Go to API Gateway console and there is nothing under "Configure Tags"

**Observed result:**
No tags
**Expected result:**
2 custom tags should be visible