Add service desk API

[AlexP11223]

Implements the Service Desk API needed for PROD-77.

I tried to keep this in similar style as the rest of the lib, while trying to do it better and more SOLID. So the API requests are grouped in <API-Group>Service classes inheriting JiraClient like the rest of the lib. Most of the entities in this part have interfaces, which e.g. don't include setters needed only for JSON mapping.

For paged queries there is Pagination similar to idealo SDK. It uses PhpStan/psalm @template generics for results. Sadly it is not supported in PhpStorm yet, so no autocompletion, etc.

The tests are mostly e2e, so they require our test Jira. Can be run via vendor/bin/phpunit tests/ServiceDesk, connection config is in .env and some config for tests (project id, ...) is in .env.phpunit. Non-e2e tests (pagination, ...) are run by CI.

Getting customer requests: not implemented because SD API cannot filter requests for the specified customer, need to use JQL from the standard API, already implemented.

Attachments: I implemented the attachment-related SD API, but looks like it is useless for our purposes because it does not allow to attach on behalf of another user, even if passing to attachment field when creating a request. 😂 The standard issue API seems to work.

One problem with this lib is that it uses Curl directly instead of PSR-18. :( There was an issue about this, possibly with some work in progress.

And also it looks like there is no easy way in Curl to upload files from a stream without a real file in fs, except building the multipart stuff manually like here. So currently we would have to create tmp files for attachments.

[XedinUnknown]

Overall, excellent work, and a superb addition to the original package!