Define electra types and apis

[ensi321]

Add electra type definition and update apis to include new types.

Also update beacon apis submodule commit to 02d595daf39943430f54aa978f88a5c50d957e64

Follow up of #101

[ralexstokes]

had one question but otherwise this looks great, thank you!!

if we update the beacon-apis submodule to at least 492bbbdbcad45249d9a8cd8c23e902c5dfe4ad28 then I think this will be final for pectra broadly

[ralexstokes]

also looks like the submodule update would help the linter errors

[ralexstokes]

lgtm, thanks!