specify amount in 'approve' method

[m-cote]

Fixes #SB-363

Description of the changes

• adds optional param amount to method approve that allows to revoke approval by setting its value to 0 or set allowance to an arbitrary amount of tokens

[github-actions[bot]]

:tada: This PR is included in version 0.8.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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