[bitbucket] multiple caches and granular cache keys

[bradrydzewski]

Bitbucket supports multiple caches and granular cache keys. Example:

definitions:
  caches:
    my-bundler-cache:
      key:
        files:
          - Gemfile.lock
          - "**/*.gemspec"
      path: vendor/bundle
    my-npm-cache:
      key:
        files:
          - package.json
      path: node_modules

[hemanthmantri]

This is similar to having multiple cache steps in a pipeline and we can provide keys for each step. We should check if we support key: {{ checksum file1, file2, file3}}