OCT-2265: Change sablier winnings endpoint

[kgarbacinski]

Description

Definition of Done

1. If required, the desciption of your change is added to the QA changelog
2. Acceptance criteria are met.
3. PR is manually tested before the merge by developer(s).
   • Happy path is manually checked.
4. PR is manually tested by QA when their assistance is required (1).
   • Octant Areas & Test Cases are checked for impact and updated if required (2).
5. Unit tests are added unless there is a reason to omit them.
6. Automated tests are added when required.
7. The code is merged.
8. Tech documentation is added / updated, reviewed and approved (including mandatory approval by a code owner, should such exist for changed files).
   • BE: Swagger documentation is updated.
9. When required by QA:
   • Deployed to the relevant environment.
   • Passed system tests.

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(1) Developer(s) in coordination with QA decide whether it's required. For small tickets introducing small changes QA assistance is most probably not required.

(2) Octant Areas & Test Cases.

[linear]

OCT-2265 Add endpoint returning the GLM giveaway amounts with dates when they are available for the withdrawal.

[aziolek]

Needs to be merged together with https://linear.app/golemfoundation/issue/OCT-2264/ui-support-for-the-glm-giveaways-receivers, or to feature branch for the story.

[kgarbacinski]

#600