Add support for grant_installation

[tsachiherman]

What ?

This PR adds support for registering a new installation.

Design considerations

The xps-gateway is the executable endpoint, that manages the rpc endpoint. It will setup an rpc server that would listen for incoming requests and perform input validation. Valid requests would be forwarded to the inbox / messaging / registry crates for method-specific implementation.

Requirements

This PR followed the design details in #22; discussion in #13 and xmtp/libxmtp#274

Note

This PR replaces #31, which has the wrong email in the commit ( i.e. unverified commit ).

[codecov]

Codecov Report

Attention: 65 lines in your changes are missing coverage. Please review.

Comparison is base (ce75da2) 78.94% compared to head (40a0e5d) 36.84%.

❗ Current head 40a0e5d differs from pull request most recent head a1f9b25. Consider uploading reports for the commit a1f9b25 to get more accurate results

Files	Patch %	Lines
xps-gateway/src/rpc/methods.rs	6.52%	43 Missing ⚠️
registry/src/registry.rs	0.00%	16 Missing ⚠️
xps-gateway/src/lib.rs	0.00%	4 Missing ⚠️
xps-gateway/src/types.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #35       +/-   ##
===========================================
- Coverage   78.94%   36.84%   -42.11%     
===========================================
  Files           9       10        +1     
  Lines         114      133       +19     
===========================================
- Hits           90       49       -41     
- Misses         24       84       +60     

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