[tests] Split out cli client tests

[townsend2010]

This is a first step to help organize the client cli tests and make them more manageable.

[codecov]

Codecov Report

Merging #2348 (9980d57) into main (862f44f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2348   +/-   ##
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  Coverage   84.83%   84.83%           
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  Files         205      205           
  Lines       10216    10216           
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  Hits         8667     8667           
  Misses       1549     1549           

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[Saviq]

This needs a rebase, and a s/2021/2022/ in the headers :)

Noice otherwise :)

[Saviq]

@townsend2010 bump?

[townsend2010]

Due to the changes I made for the authentication stuff, a MockPlatform needs to be defined before
StrictMock<MockDaemonRpc> mock_daemon in ClientTestFixture so the set_server_socket_restrictions() call in theDaemonRpc ctor can be mocked. However, due to how the singleton boiler plate is currently done, this MockPlatform definition cannot be done in a header due to the following error:

In file included from /home/townsend/multipass/multipass/tests/client/test_cli_client.cpp:18:
/home/townsend/multipass/multipass/tests/client/client_test_fixture.h:81:8: error: ‘multipass::test::ClientTestFixture’ has a field ‘multipass::test::ClientTestFixture::platform_attr’ whose type uses the anonymous namespace [-Werror=subobject-linkage]
   81 | struct ClientTestFixture : public Test
      |        ^~~~~~~~~~~~~~~~~

One of the main points of this refactoring is to move the MockDaemonRpc object into a class (ClientTestFixture) in a shared header and removing this defeats the purpose of most of this refactoring. Until this issue can be overcome, I think this should wait.