Update content resources for the London network upgrade

[samajammin]

Is your feature request related to a problem? Please describe.

We should ensure our resources are up to date re: the upcoming network upgrade - London (August 3-5, 2021): https://blog.ethereum.org/2021/07/15/london-mainnet-announcement/

Describe the solution you'd like

• update gas page to reflect to fee market structure: https://ethereum.org/en/developers/docs/gas/
  • Remove the incomplete frontmatter field
• update blocks page to explain new variable block size: https://ethereum.org/en/developers/docs/blocks/
• update transactions page to add new baseFee field: https://ethereum.org/en/developers/docs/transactions/
• update history page to show London as a historical update: https://ethereum.org/en/history/
• (depending on Sort out strategy for JSON RPC docs #3520) update JSON RPC with any endpoint updates: https://ethereum.org/en/developers/docs/apis/json-rpc/
• add CTA on developer docs section (to upgrade libraries - e.g. referencing https://github.com/ethereum/eth1.0-specs/blob/master/network-upgrades/ecosystem-readiness.md)?

Anything I'm missing here? cc @timbeiko @TrentVanEpps (what's Trent's handle)?

Describe alternatives you've considered

None

Additional context

https://www.notion.so/efdn/Update-ethereum-org-to-reflect-status-of-London-upgrade-760bc603c2544e11bd63f677ee859af3

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[timbeiko]

@tvanepps is his handle :-)

[timbeiko]

There was also the wallet filtering page that needs updating, see: #2715 (comment)

[samajammin]

Solved in #3537 #3509 #3552 #3553, closing this out.