[Persistence] Fix Persistence Module TODOs - Consolidate Postgres

[andrewnguyen22]

Objective

A general cleanup issue is needed to tackle TODO's and ensure the persistence module is usable/readable by consolidating PostgresContext and PostgresDb as part of #172.

Origin Document

Should follow issue-#128, issue-#105, issue-#147 and issue-#148 the persistence module is messier and more difficult to understand than the developers would want for organic external contribution.

Goals / Deliverables

• Run `log.
• Finish outstanding TODO's to ensure end-to-end functionality
• Consolidate PostgresContext and PostgresDb like so:

type PostgresContext struct {
	height int64
	tx         pgx.Tx
	blockstore kvstore.KVStore	
}

• Avoid exposing PostgresContext and/or PostgresDb for testing purposes

General issue checklist

• Update the appropriate CHANGELOG
• Update the README
• If applicable, update the source code tree explanation
• If applicable, add or update a state, sequence or flowchart diagram using mermaid
• Update any relevant global documentation & references
• Document small issues / TODOs along the way

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Creator: @andrewnguyen22
Co-creator: @Olshansk

[Olshansk]

Outside of the context of this, just figured I'd share that after we do a team massive cleanup of all our TODO tags, we can also automate it via #144.

@andrewnguyen22 Please also attach issues to the V1 Dashboard Projects so we can see it all in one place

[andrewnguyen22]

Good call ^

[Olshansk]

@andrewnguyen22 Per the discussion last friday, I'll take on persistence in the cleanup phase. I'll submit every bullet point here (and others) as a separate PR.