MYSQL Extention isn't enabled in webapp linux managed mysql template

### Issue Details
When a webapp linux managed mysql template is created the Mysqli and PDO_MySQL extensions aren't enabled and no simple way is provided to enable them.

### Repro steps
1. run install PHP webapp-linux-managed-mysql
2. configure the deployment center with a bitbucket repository
3. Add a single page contains phpinfo() to the repo and push it.
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4. open php info page
5. you will not find the any of MySQL extensions enabled and no simple way to enable it.

Start by locating the webapp-linux-managed-mysql template referenced in the install command and review how PHP is configured for the deployed Linux web app. Deploy the template, use the reported phpinfo() page to verify the mysqli and PDO_MySQL extensions, and consider the issue complete when they are enabled or a documented, simple enablement path is provided.

Written by the indexing model from the issue text.