feature: pricing policy

[IvayloAtanasov]

Changes

• "Approve Fee" button for each plugin in the marketplace web app
• plugin_pricings table to store pricing policies signed by users
• GET /plugin/:pluginType/pricing-policy on plugin (verifier endpoint also exists but is not needed). FE would need it in order to check if user signed the pricing policy, before giving permission to the user to use plugin features.
• POST /plugin/:pluginType/pricing-policy on both plugin (create) and verifier (sync). Create signed pricing record. Verifier also check of the signed policy matches the policy definition in plugin. To be used upon plugin install.
• generate fee ERC20 transfer transaction on every dca policy schedule trigger
• validate fee transaction in verifier
• fee wallet EOA to collect all dca plugin fees

Implementation notes

• fees only implemented for DCA policy
• only per tx fee type is implemented
• fees are charged on top of assigned transactions, not deducted from the amount spent with each trigger