Add state_override argument to estimate_gas

[kclowes]

What was wrong?

As of geth 1.12.1, estimate_gas allows a state_override argument.

How can it be fixed?

Allow eth.estimate_gas to take the state_override param. Can follow the existing eth.call implementation.

[reedsa]

Planning this as part of v7 (#2854) since this requires an upgrade of geth which appears to be a bit more involved.

[fselmo]

no longer v7 only since #3209 was merged