handle multi pkg & mono repo structure

[kuldeepkeshwar]

Configure bot for multiple builds or mono repo setup

In the case of multiple builds,

size-files:
    - sizes-browser.json
    - sizes-server.json

In case of multiple packages in a single repo or mono repo

size-files:
    - dir: packages/a
      filename: sizes-a.json
    - dir: packages/b
      filename: sizes-b.json
    - dir: packages/c
      filename: sizes-c-browser.json
    - dir: packages/c
      filename: sizes-c-server.json