Add an end_block field in manifest

[0xmovses]

Brought up by @ra0x3 in team sync today, users should be able to add an end_block field, to determine when an indexer should stop indexing. Without this, all indexers by default will run and listen for events on new blocks indefinitely.

• Add a new field in the manifest file, update Manifest struct and add the logic necessary to achieve this functionality.

• Additionally, if no end_block is set, we should display a very clear warning message when the indexer starts, notifying users that this index will run until explicitly stopped.

• In the PR an e2e test and documentation should be included.