[POC] Polygon payment driver support

[kmazurek]

Effect of work on #551

This is a proof-of-concept support for the Polygon driver in goth tests. Currently it requires yagna to have polygon (or, more specifically, erc20-mumbai-tglm)

Current assumptions and limitations:

1. Running tests with this version of goth requires Polygon testnet (specifically: erc20-mumbai-tglm) to be set as the default driver in yagna. Such a build of yagna is available on branch km/polygon-default (Make erc20 the default driver. Enable polygon. yagna#1650).
2. zksync support is currently removed as it's currently not possible to choose the payment setup to be used by goth.
3. Network name (mumbai) is hardcoded in a few places, this is related to 2.

Known issues:

1. Payment confirmations are broken. This is probably related to how Ganache (local blockchain spawned as part of goth's compose network) handles block creation (@maaktweluit might know more about this).

[shadeofblue]

@zakaprov soo....

we've discussed matters a bit and the current consensus is that:

1. zksync is not going away, even after we release polygon support and even after we make it a default, we'll still want to support it as an option
2. for the time being (i.e. beta.4 release), zksync/rinkeby will remain the default for the requestors
3. to enable polygon/mumbai properly, we'll need a proper faucet that can be used to automatically feed the requestors with GLM and MATIC tokens so the UX for someone wanting to try Golem for the first time remains smooth...
4. probably the faucet will be ready soon but afaik, we still won't want to switch to polygon/mumbai as the default in beta.4

that all means that for now, we don't most likely won't need or want to merge this pull request here...

BUT

at the same time, the real issue I see here is that we're not testing our payment platforms properly ...

thus, I think that in the short term, it should be our priority to enable goth to be able to vary the payment platform used on a per-test basis so that we could have at least a single basic integration test using each of the payment platforms enabled in yagna... -> erc20/rinkeby, zksync/rinkeby, erc20/mumbai

I'll add that as a "bottom drawer" task in Miro - please do plan to have it worked on in our next iteration