TrustStore: Resolver handles certificate chains

[oncilla]

This PR adds the capability to resolve certificate chains to the
resolver.

fixes #3469

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This change is 

[lukedirtwalker]

Reviewed 3 of 4 files at r1, 2 of 2 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @oncilla)

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go/lib/infra/modules/trust/v2/resolver_test.go, line 258 at r1 (raw file):

			r := trust.NewResolver(m.DB, m.Inserter, m.RPC)
			dec, err := r.Chain(context.Background(), test.ChainReq, nil)
			if test.ExpectedErr != nil {

everything below can be simplified to:

			xtest.AssertErrorsIs(t, err, test.ExpectedErr)
			if test.ExpectedErr == nil {
				assert.Equal(t, expected, dec)
			}

[oncilla]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @lukedirtwalker)

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go/lib/infra/modules/trust/v2/resolver_test.go, line 258 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

everything below can be simplified to:

			xtest.AssertErrorsIs(t, err, test.ExpectedErr)
			if test.ExpectedErr == nil {
				assert.Equal(t, expected, dec)
			}

Done.

[lukedirtwalker]

Reviewed 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved

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go/lib/infra/modules/trust/v2/resolver_test.go, line 258 at r3 (raw file):

			dec, err := r.Chain(context.Background(), test.ChainReq, nil)
			xtest.AssertErrorsIs(t, err, test.ExpectedErr)
			assert.Equal(t, expected, dec)

💯 for also fixing this :)