Prepare 2.15.0.dev0

[Eric-Arellano]

[ci skip-rust]

[Eric-Arellano]

Internal (put these in a PR comment for review, not the release notes)

• Refactor PythonBootstrap type (#16684)

• Bootstrap scheduler ignores invalid BUILD file symbols when parsing (#16661)

• Fix LintGoal.activated() to consider fmt goal (#16674)

• Wire BUILD file formatters in lint (#16666)

• increase LMDB size to fix a test on Apple M1 (#16672)

• Fix clippy lints after Add support for passing multiple input params to a @rule Get #16668 (#16671)

• Format build files (#16650)

• Support Docker custom tags via plugin hook (#16662)

• Remove orphaned Get parsing code. (#16658)

• Replace union hierarchy tricks with direct class traversal (#16657)

• Don't register non-union subclasses of unions as union members (#16645)

• Prepare 2.12.1rc4 (#16637)

• Prepare 2.13.0rc2 (#16636)

• Bump futures-core from 0.3.21 to 0.3.23 in /src/rust/engine (#16579)

• Bump shellexpand from 2.1.0 to 2.1.2 in /src/rust/engine (#16474)

• Bump chrono from 0.4.19 to 0.4.20 in /src/rust/engine (#16475)

• Bump strum_macros from 0.24.2 to 0.24.3 in /src/rust/engine (#16473)

• Make DependencyKey a concrete type (#16628)

• Keep --process-cleanup until 3.0 (#16613)