Adds coin select flags to defid with option to override from CLI

[Jouzo]

Summary

• Adds coin select flags to defid
• Adds GetOptionalBoolArg for when a flag should not have any default value. This is here used to override defid flag iff flag is also set via defi-cli

Examples

defid -walletfastselect=1

defi-cli sendtoaddress <address> 1

• Will use value from defid

---

defid -walletfastselect=1

defi-cli -walletfastselect=0 sendtoaddress <address> 1

• Value will be overridden and set to 0 from defi-cli

Flags

-walletfastselect - Faster coin select - Enables walletcoinoptskipsolvable and walletcoinopteagerselect. This ends up in faster selection but has the disadvantage of not being able to pick complex input scripts. Default: false

-walletcoinoptskipsolvable - Coin select option: Skips IsSolvable signable UTXO check. Default: false

-walletcoinopteagerselect - Coin select option: Take fast path and eagerly exit on match even without having through the entire set. Default: false

[prasannavl]

CreateDefault will still always initialize everything. Also ToHTTPHeader shouldn't be calling out to the gArgs. It should only be contained within the FromArgs.

Other motivations behind keeping ToHTTPHeader, FromHTTPHeader dependency-free, is that they are now individually testable. Shouldn't depend on gArgs that destroys test ability of these methods. Let's use FromArgs to handle this.

We'll need to tweak this a bit.

[prasannavl]

Added changes here: https://github.com/DeFiCh/ain/compare/pvl/coinselect-cli?expand=1. Believe that should provide a better base and mostly solve it.

To-do on that branch:

• Find the best way to detect defi-cli or defid (best to use it statically if we have an optional define from somewhere)
• Adapt rest of the coinselect usage to work with optional
• Port the request metadata pass on to the rest of methods in this branch

[prasannavl]

LGTM