Tracking issue for Tokio 1.x

[trevyn]

Tokio 1.0 was released in December 2020, and the ecosystem is starting to stabilize around it. While the 0.2.x branch is still widely used, it seems clear that it will only receive critical fixes going forward.

This issue is to track our progress in making this upgrade and the upgrades of other Tokio-related dependencies: reqwest, hyper, etc.

• Verify that this needs to be synchronized with an update to grin-wallet and would be a semver-major bump in order not to have incompatible versions of Tokio.
• Wait for Replace custom hyper client with reqwest grin-wallet#593 to be merged so that we have a stable starting point.