Support for AWS Lambda on Self Hosted

## Important Details

How are you running Sentry?

On-Premise w/ Docker, version 21.3.0 96d5172

## Description

Clicking on `Go to AWS` button on AWS Integration page goes to TemplateURL missing error.


## Steps to Reproduce

1. Go to Settings
2. Navigate to Integration from left sidebar.
3. Click on `Add Integration` for AWS Lambda
4. Pop Up appears with

5. Click on `Go To AWS`
6. Login with AWS credentials
7. CloudFormation Page appears with the error since the templateURL in the URL is blank.

Good items to include here include:

- Include a stacktrace or other logs when relevant
- Include a redacted version of your configuration (`sentry.conf.py` and `config.yml` files) when relevant

### What you expected to happen

templateURL is supposed to be populated with link to the CloudFormation template file. But it is indeed blank.
`stackName=Sentry-Monitoring-Stack&templateURL=`