feat: abci client type now an explicit config setting

[JimLarson]

Description

Refs: Agoric/agoric-sdk#9224

Add an explicit entry for abci-client-type in the TOML file. The setting can be done in the file but is overridden by when the command-line flag is set.

Note that this entry is unlike the other entries in the "base config" part of the TOML file, in that there are no BaseApp.Get/SetABCIClientType() methods, option helpers, etc. This makes it more like the various start command flags that do not have explicit config fields, e.g. --with-tendermint or --trace-store. This seems appropriate for a setting that is used near the "top" of the start command.

Note that even without this change, the option can be set in the config/app.toml file. This just makes the entry part of the automatically-generated TOML file.

Note that the default value is now specified both in the flag definition and in the default config constructor, as some of the other flags are. It's confusing to think about which one takes precedence, so they should just be kept in sync.

Tested the following:

• start with default toml file which includes and explicit entry to the default "committing" value
• start with an illegal value - fails as expected
• start with non-default valid value "local"
• start with line removed from app.toml
• override with flag set to an illegal value - fails as expected
• override with flag set to "committing"
• restore app.toml entry and override with a different legal value
• override with illegal flag - still fails as expected.

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[mhofman]

No way to reference the "other" default value ?

[JimLarson]

Not where it is now - circular imports. Let me see if I can do the reference the other way - or at least add cross-reference comments.

[JimLarson]

Done. Now the options and default are defined in one place - the config package. (The server/types package seems like the better place, but it imports server/config.)

[JimLarson]

D'oh! It would help if I actually used the constant I just defined. Actually done now.