`CoinsToSpend` query should return selected coins even if the amount cannot be covered

[rafal-ch]

Currently, when the CoinsToSpend query cannot find enough coins it returns an error:

    #[error("the target cannot be met due to no coins available or exceeding the {max} coin limit.")]
    InsufficientCoinsForTheMax {
        asset_id: AssetId,
        collected_amount: u128,
        max: u16,
    },

The new behavior should be:

1. add new field to the query, for example: allow_partial: bool. If this field is set to true, then:
   • do not return an error
   • return coins that we were able to find even if they do not satisfy the query

Definition of Done:

1. InsufficientCoinsForTheMax error is never thrown (from both indexed and non-indexed coins to spend algorithm implementations) if the new flag is set
2. Tests are updated to cover system behavior with this new flag
3. Indexation documentation is updated: https://www.notion.so/fuellabs/Indexation-1932f2293f31806b87c1ef8160d3acd7

[rafal-ch]

PR ready, I'll update the necessary documentation after it is merged since there could be some other changes required.

Also, the potential follow-up issue will be created when the PR is merged.