Added documentation for get_block_timestamp, get_block_round and get_block_epoch

[janniksam]

Description

Added documentation for

• get_block_timestamp
• get_block_round
• get_block_epoch

Did you test the changes locally ?

• [x] yes
• [ ] no

Which category (categories) does this pull request belong to?

• [ ] document new feature
• [ ] update documentation that is not relevant anymore
• [x] add examples or more information about a component
• [ ] fix grammar issues
• [ ] other