define block hash provider and default impl using frame_system

[vedhavyas]

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Description

• What does this PR do?
  Defines a Block Hash Provider for MMR pallet instead of using frame_system::Pallet::block_hash directly
• Why are these changes needed?
  Described here - Pallet-MMR should use custom block_hash getter instead of using frame_system::block_hash for non-canonicalised blocks paritytech/polkadot-sdk#4062
• How were these changes implemented and what do they affect?
  This add a new type to MMR config and with provided DefaultProvider, should not change anything on the logic wise.

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Fixes paritytech#4062
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The companion PR to upstream is approved and this commit will not necessary during the next upgrade, given upgrade contains the changes from the upstream PR.

[vedhavyas]

@nazar-pc seems like the rust-fmt check failed due to unrelated changes to this PR.
Is the incorrect formatting expected or should I fix it ?

[nazar-pc]

As long as it compiles I'm okay with it. Can we wait for upstream PR to be merged first? Ideally we'd land the final version, but I understand we may need it sooner.

[vedhavyas]

As long as it compiles I'm okay with it. Can we wait for upstream PR to be merged first? Ideally we'd land the final version, but I understand we may need it sooner.

That is fair. Its in the merge queue now. Will this one once upstream PR is merged into main