Use federation sync config in syncer

[ffranr]

In this PR we modify the simple syncer and the federation envoy such that they use the federation sync configuration.

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This change is 

[ffranr]

In the fed sync config we differentiate between import and export syncing. This PR doesn't currently handle that nuance. We sync if both import and export is enabled.

[Roasbeef]

• Examine export/insert in the rpc calls, reject read for export, opposite for import
• Only examine insert for the syncer
• Scratchup config, if only for itests -- --universe.public_access, allows insert+export global -- (--universe.public_issuance, --universe.public_proofs)

[Roasbeef]

Reviewed 9 of 9 files at r2, all commit messages.
Reviewable status: 7 of 9 files reviewed, 6 unresolved discussions (waiting on @ffranr and @guggero)

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rpcserver.go line 3272 at r3 (raw file):

	// TODO(roasbeef): query may return multiple proofs, if allow key to
	// not be fully specified
	proof := proofs[0]

if len(proofs) == 0 {
return universe.ErrNoNUniverseProofFound
}]

Code quote:

	// TODO(roasbeef): query may return multiple proofs, if allow key to
	// not be fully specified
	proof := proofs[0]

[Roasbeef]

Reviewed 2 of 2 files at r3.
Reviewable status: 8 of 9 files reviewed, 7 unresolved discussions (waiting on @ffranr and @guggero)

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universe/auto_syncer.go line 490 at r3 (raw file):

	// Obtain the general and universe specific federation sync configs.
	syncConfigs, err := f.QuerySyncConfigs(ctx)

Missing error check.