Add a tooltip explanation for each field on the contracts data table

Explanation of fields for hostd:

General

• contract ID: the ID of the contract
• status: the current lifecycle stage of the contract (pending, active, successful, failed)
• data size: the amount of data stored in the contract (in bytes)
• merkle root: the merkle root of the data stored in the contract (used for proofs)

Time

• timeline: a timeline of the contract's life
• start date: the date the contract was created
• expiration date: the estimated date the contract will expire
• payout date: the estimated date the host will receive the payout

Usage

• payout: the total payout the host will receive upon contract expiration (revenue + locked collateral)
• remaining renter funds: the remaining Siacoin the renter has to spend
• locked collateral: the amount of Siacoin the host locked in collateral
• risked collateral: the amount of Siacoin the host will burn if the contract fails
• total usage: the total spending of the renter
• storage usage: the amount spent on storage
• ingress usage: the amount spent on uploading data
• egress usage: the amount spent on downloading data
• account funding usage: unspent ephemeral account balance
• rpc usage: the amount spent on RPC calls

Locate the contracts data table entry point in the web packages and inspect how its fields are rendered. Add tooltips for each listed field using the explanations in the issue, then verify that every field displays the corresponding explanation in the table.