[Staking] Match NFT attribute key/value to pallet-nfts spec

[DidacSF]

Description

This pallet replaces both NFT attribute key and value for BoundedVec with configurable bound limits, like pallet-nfts.

Type of changes

• build: Changes that affect the build system or external dependencies (eg, Cargo, Docker)
• ci: Changes to CI configuration
• docs: Changes to documentation only
• feat: Changes to add a new feature
• fix: Changes to fix a bug
• refactor: Changes that do not alter functionality
• style: Changes to format the code
• test: Changes to add missing tests or correct existing tests

Checklist

• Tests for the changes have been added
• Necessary documentation is added (if appropriate)
• Formatted with cargo fmt --all
• Linted with cargo clippy --all-features --all-targets
• Tested with cargo test --workspace --all-features --all-targets

[codecov]

Codecov Report

Patch coverage: 25.00% and no project coverage change.

Comparison is base (ff3d855) 75.81% compared to head (dedd25d) 75.81%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #344   +/-   ##
========================================
  Coverage    75.81%   75.81%           
========================================
  Files           33       33           
  Lines         3444     3444           
========================================
  Hits          2611     2611           
  Misses         833      833           

Files Changed	Coverage Δ
pallets/ajuna-nft-staking/benchmarking/src/lib.rs	0.00% <0.00%> (ø)
pallets/ajuna-nft-staking/src/lib.rs	80.00% <0.00%> (ø)
pallets/ajuna-nft-staking/src/contracts.rs	93.54% <100.00%> (ø)

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[darkfriend77]

Let's get this up and running.