Support Omitted Blocks

[patrick-ogrady]

Blocked by: coinbase/mesh-sdk-go#91

This PR adds support for storing omitted blocks and for querying blocks by only index or only hash (previously had to provide both block hash and index).

Warning

This PR changes how data is persisted to storage. When you upgrade, you will need to delete any cache you were using previously.

Changes

• Update syncer to support omitted blocks (Support Omitted Blocks mesh-sdk-go#91)
• Add tests to storage for omitted blocks
• Add lookup block by index

[coveralls]

Pull Request Test Coverage Report for Build 3382

• 58 of 71 (81.69%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.4%) to 71.993%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/storage/block_storage.go	58	71	81.69%

Files with Coverage Reduction	New Missed Lines	%
pkg/storage/block_storage.go	3	66.18%

Totals
Change from base Build 3360:	0.4%
Covered Lines:	1622
Relevant Lines:	2253

---

💛 - Coveralls

[yfl92]

nit: feels like it's more idiomatic to evaluate if err != nil first

        _, err := h.blockStorage.GetBlock(ctx, types.ConstructPartialBlockIdentifier(block))
	if err != nil {
		if errors.Is(err, storage.ErrBlockNotFound) {
			return false, nil
		}

		return false, err
	}

	return true, nil

[patrick-ogrady]

Although I agree it is more idiomatic to do if err != nil first, I think it is more preferable to avoid nesting conditionals.