### 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
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