Validator schema upgrade

[charithabandi]

Legacy branch : (v0)

• Without schema_version table
• No Join expiry in Join requests

V1:

• Introducing schema_version table that tracks the version the database is at
• added expiresAt column to the join_reqs
• set the API version to 1

Process:
We check existence of the version and data tables and decide the version the database is at and run appropriate upgrades or initializations. Below are the scenarios that can occur:

1. Fresh DB start, no version and data tables ----> Do regular initialization, set the version to currentVersion.
2. Legacy mode: data tables exist but not version. ----> Add version table, set the version to currentVersion and run Migrations to update the join_reqs table
3. Data and version tables exist, and we are on correct version ----> do regular initialization
4. Future purposes: If we are on lower versions -> run migrations

[charithabandi]

#318 Use this PR instead