Governance support for pindexer (#4708)

## Describe your changes

This adds a governance module to `pindexer`, along with tiny changes to
`pd`'s governance events to fully support it.

## Checklist before requesting a review

- [X] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

> The only changes to `pd` are changes to events emitted, which do not
break consensus.

---------

Co-authored-by: Henry de Valence <hdevalence@penumbralabs.xyz>
Co-authored-by: Lucas Meier <lucas@cronokirby.com>

crates/bin/pindexer/Cargo.toml

@@ -19,10 +19,11 @@ penumbra-shielded-pool = {workspace = true, default-features = false}
 penumbra-stake = {workspace = true, default-features = false}
 penumbra-app = {workspace = true, default-features = false}
 penumbra-dex = {workspace = true, default-features = false}
+penumbra-governance = {workspace = true, default-features = false}
 penumbra-num = {workspace = true, default-features = false}
 penumbra-asset = {workspace = true, default-features = false}
 penumbra-proto = {workspace = true, default-features = false}
+tracing = {workspace = true}
 tokio = {workspace = true, features = ["full"]}
 serde_json = {workspace = true}
 sqlx = { workspace = true, features = ["chrono", "postgres"] }
-tracing = {workspace = true}