Doc : update Alpha changelog

Context

Updating Alpha changelog to reflect protocol and environment changes merged into master before 13th of March.

The following MRs have touched src/proto_alpha/lib_protocol or src/lib_protocol_environment/sigs/v*/ since the last update of Alpha changelog (!7917 (merged)).

• !7536 (merged) - internal renaming only
• !7650 (merged)
• !7712 (merged) - tests only
• !7730 (merged)
• !7815 (merged) - already included in change log
• !7833 (merged) -
• !7892 (merged) - tests only
• !7893 (merged) - tests only
• !7915 (merged) - formatting only
• !7954 (merged)

The list was generated using the following commands:

$ git log --reverse --merges --full-history f9675b19..c8278f5f -- src/proto_alpha/lib_protocol/ src/lib_protocol_environment/sigs/v*/ | grep 'See merge request' | sort

Manually testing the MR

Please read the description of changes.