### Summary
Tracking issue: https://github.com/wormhole-foundation/wormhole-explorer/issues/254
For all chains except Solana, the data in `globalTransactions.sourceTx` was somewhat duplicated, since we already had that data in the `vaas` collection.
This pull request changes the `tx-tracker` service so that no redundant data will be written, and also changes the API to look up the data from the `vaas` collection instead.
The responses from the endpoint `/api/v1/global-tx` will no longer contain the field `originTx.from`.
### Summary
The tx-tracker service was exceeding node RPC rate limits, which caused it to fail.
This pull request changes the APIs upon which the service depends to avoid the same issue in the future.
Also, the backfiller job has been updated accordingly.
Tracking issue: https://github.com/wormhole-foundation/wormhole-explorer/issues/205
### Summary
This pull request adds a new component under the directory `txtracker`.
This component retrieves information about portal token bridge transfers (i.e.: sender address, receiver address, timestamp), and persists the data in MongoDB.
### Chains supported
The blockhains currently supported are:
* Terra (27% of outgoing transfers)
* Solana (25%)
* BSC (25%)
* Eth (14%)
* Polygon (4%)
The remaining chains will be added iteratively as needed.
agodnic