Retry on anaconda.org connection errors

[pavelzw]

Sometimes i get errors like this:

Error: Event { fields: ValueSet { message: Error building package: failed to setup test environment: Request error: error sending request for url (https://conda.anaconda.org/conda-forge/linux-64/mumps-include-5.6.2-ha770c72_4.conda): connection closed before message completed, callsite: Identifier(0x5609df8de0d0) }, metadata: Metadata { name: "event src/main.rs:732", target: "rattler_build", level: Level(Error), module_path: "rattler_build", location: src/main.rs:732, fields: {message}, callsite: Identifier(0x5609df8de0d0), kind: Kind(EVENT) }, parent: Current }
 × error Error building package: failed to setup test environment: Request error: error sending request for url (https://conda.anaconda.org/conda-forge/linux-64/
 × error mumps-include-5.6.2-ha770c72_4.conda): connection closed before message completed
Error:   × failed to setup test environment: Request error: error sending request for
  │ url (https://conda.anaconda.org/conda-forge/linux-64/mumps-include-5.6.2-
  │ ha770c72_4.conda): connection closed before message completed
  ├─▶ Request error: error sending request for url (https://
  │   conda.anaconda.org/conda-forge/linux-64/mumps-include-5.6.2-
  │   ha770c72_4.conda): connection closed before message completed
  ├─▶ error sending request for url (https://conda.anaconda.org/conda-forge/
  │   linux-64/mumps-include-5.6.2-ha770c72_4.conda): connection closed before
  │   message completed
  ╰─▶ connection closed before message completed

Since this is only a temporary issue and is fixed on a rerun, I would prefer if rattler just retried downloading the packages on these kinds of errors and only create an issue when it's actually failing multiple times (maybe also use exponential backoff?)

[nichmor]

I like this idea!