Fee foreign reserve

[grarco]

Describe your changes

Closes #4496.

Changes the base fee logic: burns it if the fee token is the native one and sends it to PGF otherwise. For now the base fees for non-native tokens is sent to the PGF internal account. An alternative would be to create a new internal account for this specific purpose, here's a list of possible pros of both solutions:

• PGF account
  • less code required
  • pgf cannot spend non-native tokens, so for now this is safe
• New internal account
  • better logical separation of funds (not really user-related, more for devs), especially useful if we wanted to keep track of the original block proposers from whom these fees are coming

Checklist before merging

• [x] If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• [x] If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies: https://github.com/anoma/namada-docs/pull/445
• [x] If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies: https://github.com/anoma/namada-indexer/pull/380