shlinkio/shlink v1.21.0 on GitHub

#118 API errors now implement the problem details standard.
In order to make it backwards compatible, two things have been done:
- Both the old error and message properties have been kept on error response, containing the same values as the type and detail properties respectively.
- The API v2 has been enabled. If an error occurs when calling the API with this version, the error and message properties will not be returned.
After Shlink v2 is released, both API versions will behave like API v2.
#575 Added support to filter short URL lists by date ranges.
- The GET /short-urls endpoint now accepts the startDate and endDate query params.
- The short-urls:list command now allows --startDate and --endDate flags to be optionally provided.
#338 Added support to asynchronously notify external services via webhook, only when shlink is served with swoole.
Configured webhooks will receive a POST request every time a URL receives a visit, including information about the short URL and the visit.
The payload will look like this:
```
{
  "shortUrl": {},
  "visit": {}
}
```
The shortUrl and visit props have the same shape as it is defined in the API spec.

#492 Updated to monolog 2, together with other dependencies, like Symfony 5 and infection-php.
#527 Increased minimum required mutation score for unit tests to 80%.
#557 Added a few php.ini configs for development and production docker images.

#570 Fixed shlink version generated for docker images when building from develop branch.