Feature/Xline client maintenance

[bsbds]

Implement maintenance client in xline-client

Please briefly answer these questions:

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)

• what changes does this pull request make?

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)

[codecov]

Codecov Report

Patch coverage: 13.17% and project coverage change: -1.81 ⚠️

Comparison is base (9c1be4b) 54.79% compared to head (2289264) 52.99%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #323      +/-   ##
==========================================
- Coverage   54.79%   52.99%   -1.81%     
==========================================
  Files          87       89       +2     
  Lines       12736    13258     +522     
  Branches    12736    13258     +522     
==========================================
+ Hits         6979     7026      +47     
- Misses       5305     5783     +478     
+ Partials      452      449       -3     

Impacted Files	Coverage Δ
benchmark/src/lib.rs	100.00% <ø> (ø)
benchmark/src/runner.rs	8.61% <0.00%> (+0.43%)	⬆️
curp-external-api/src/lib.rs	100.00% <ø> (ø)
curp-test-utils/src/lib.rs	47.05% <ø> (-9.04%)	⬇️
curp/src/lib.rs	100.00% <ø> (ø)
curp/src/rpc/mod.rs	26.66% <ø> (ø)
curp/src/server/cmd_board.rs	41.30% <0.00%> (ø)
curp/src/server/mod.rs	0.00% <ø> (ø)
engine/src/lib.rs	100.00% <ø> (ø)
utils/src/lib.rs	87.41% <ø> (ø)
... and 18 more

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