fix: configure initial release version

[lusu007]

Summary

• configure Release Please's official initial-version option as 0.1.0
• keep the bootstrap manifest empty until Release Please merges its first release PR

Evidence

• with the predeclared manifest, Release Please proposed 0.2.0
• with an empty manifest and no initial-version, the simple releaser proposed 1.0.0
• the explicit initial-version removes that ambiguity while Release Please remains responsible for the tag and release

Verification

• both Release Please JSON files parse with jq
• initial-version resolves to exactly 0.1.0
• git diff check passes