Implement getting Saving positions

[dinosaurchi]

Overview

Introduced:

• NewSavingFixedProjectPositionsService
• NewSavingFlexibleProductPositionsService

[dinosaurchi]

hi @adshao , can you help to review and merge this PR?

[codecov[bot]]

Codecov Report

Merging #416 (1bcd4fb) into master (8b5878a) will decrease coverage by 0.02%. The diff coverage is 67.30%.

@@            Coverage Diff             @@
##           master     #416      +/-   ##
==========================================
- Coverage   70.02%   70.00%   -0.03%     
==========================================
  Files          74       74              
  Lines        6838     6890      +52     
==========================================
+ Hits         4788     4823      +35     
- Misses       1550     1560      +10     
- Partials      500      507       +7     

Impacted Files	Coverage Δ
v2/staking_service.go	36.14% <ø> (ø)
v2/savings_service.go	83.42% <64.58%> (-7.13%)	:arrow_down:
v2/client.go	81.05% <100.00%> (+0.23%)	:arrow_up:

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