Add an option to the file method to checksum

[jordeu]

Description

Adds the checksum option to the file method that allows to verify that a downloaded file at the stage directory is valid.

Notes:

• this is only verified the first time that the file is downloaded into the local stage folder
• this is only supported by XPath filesystem (HTTP, HTTPS and FTP protocols).

Guidelines for testing

1. Checkout this branch
2. make clean compile
3. Run ./launch.sh run jordeu/nf-tests -r checksum (pipeline should success)
4. Run ./launch.sh run jordeu/nf-tests -r checksum --md5 8ddd8be4b179a529afa5f2ffae4b98 (pipeline should fail).

Example fail output:

$ ./launch.sh run jordeu/nf-tests -r checksum --md5 8ddd8be4b179a529afa5f2ffae4b98
N E X T F L O W  ~  version 23.10.0
Launching `https://github.com/jordeu/nf-tests` [jolly_pare] DSL2 - revision: 81ac09fbc7 [checksum]
[-        ] process > MD5      -
[-        ] process > SHA1 (1) -
[-        ] process > SHA256   [  0%] 0 of 1
ERROR ~ Error executing process > 'MD5 (1)'

Caused by:
  Invalid checksum at /jordeu/nf-tests/checksum/hello.md5


 -- Check '.nextflow.log' file for details

When it fails you can check the computed checksums at the logs:

$ cat .nextflow.log | grep "Expected checksum"
Oct-17 15:31:45.429 [FileTransfer-2] DEBUG nextflow.file.FileHelper - Expected checksum 'sha1::a0b65939670bc2c010f4d5d6a0b3e4e4590fb92b' matches computed one
Oct-17 15:31:45.497 [FileTransfer-3] DEBUG nextflow.file.FileHelper - Expected checksum '8ddd8be4b179a529afa5f2ffae4b98' found '8ddd8be4b179a529afa5f2ffae4b9858'
Oct-17 15:31:45.548 [FileTransfer-1] DEBUG nextflow.file.FileHelper - Expected checksum 'sha256::03ba204e50d126e4674c005e04d82e84c21366780af1f43bd54a37816b6ab340' matches computed one

Closes #2491

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