Add Etherscan-visible versioning to pools

[EndymionJkb]

We have a versioning system in the /deployments package and readme's that labels each deployment with a date, includes the complete build info, and often indicates a version in the name (e.g., gauge-adder-v2). Of course, none of this is known by Etherscan, so finding out which version a pool is could involve checking all the factories to find which one deployed it, then noting the date the factory was deployed, and looking it up in the repo docs, which is all manual and fairly cumbersome.

We could change the name of the contract itself, which would be visible in Etherscan - but we don't generally want to change the names of the contracts unless it is truly different (e.g., StablePool -> ComposableStablePool). If we're just fixing a bug or updating a dependency (e.g., Aave v2 to v3), the name should stay the same.

We could also have an external contract registry with metadata, including this information - and we may well do this at some point - but that's too heavyweight for now.

So the consensus solution is to add a version method to all pools that returns a string. Alternatively, if we want an easily machine-readable numeric value (vs parsing it out of a string), we could add a versionNumber: 1,2,3,4,... and a versionName, which might be a string identifying the task id (e.g., '20221111-authorizer-adaptor-entrypoint'). Then it would be trivial to find the correct deployment from Etherscan

[nventuro]

#2032 added this for AaveLinear - we'll likely want to have this in NewBasePool and propagate it to all other pool types.