chore: enable bump-minor-pre-major for pre-1.0 releases (#79)

Configures release-please to bump 0.x.y → 0.(x+1).0 on a BREAKING
CHANGE: footer instead of bumping straight to 1.0.0. The default
release-please behavior for any 0.x.y release-type:simple package is
that BREAKING CHANGE triggers a 1.0.0 bump; bump-minor-pre-major:true
overrides that to "BREAKING CHANGE while < 1.0.0 only bumps minor".

Why now: PR #77 (the v0.3.0 rollup) carries a BREAKING CHANGE: footer.
release-please opened release PR #78 proposing 1.0.0. We closed #78
without merging — the manifest is still 0.2.3, no tag was cut. With
this config change, the next release-please run will recompute against
main and propose 0.3.0 instead of 1.0.0.

Schema verification: bump-minor-pre-major is a documented field on the
release-please config schema at both the top level (acts as default
for all packages) and the per-package level. Verified against
https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json
and the implementation in release-please src/manifest.ts:1746-1747
which reads pathConfig.bumpMinorPreMajor ?? defaultConfig.bumpMinorPreMajor.
Setting both explicitly for defense-in-depth.

This config is evaluated against current commits at run time, so it
applies retroactively to the BREAKING CHANGE: footer already on main.
No need to amend the rollup commit or cherry-pick history.

Note: the closed PR #78 still has the autorelease: pending label. That
label only matters on OPEN PRs; release-please's matcher
(findOpenReleasePullRequests) ignores closed ones unless they carry
autorelease: snooze. PR #78 is therefore invisible to the next run,
which will open a fresh release PR with the corrected 0.3.0 proposal.

Author: StefanSteiner

release-please-config.json

@@ -2,11 +2,13 @@
   "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
   "include-component-in-tag": false,
   "separate-pull-requests": false,
+  "bump-minor-pre-major": true,
   "packages": {
     ".": {
       "release-type": "simple",
       "component": "hyper-api-rust",
       "changelog-path": "CHANGELOG.md",
+      "bump-minor-pre-major": true,
       "extra-files": [
         { "type": "toml", "path": "Cargo.toml", "jsonpath": "$.workspace.package.version" },
         { "type": "generic", "path": "hyperdb-api-core/Cargo.toml" },