feat: add `--send` to `contract invoke` and default to only sending transaction if there are writes in the ledger footprint

[willemneal]

What

See initial discussion here: https://github.com/stellar/stellar-cli/issues/225

Why

Currently users must opt in to not sending a transaction with --is-view. This deprecates --is-view and flips the default to only send if there are writes in the ledger footprint returned by the simulation.

It improves UX because now when making a view call a user must wait for the transaction be complete vs viewing the simulation result.

Known limitations

[TODO or N/A]