Specify available RSE in RucioRemoteBackend

[dachengx]

Before you submit this PR: make sure to put all operations-related information in a wiki-note, a PR should be about code and is publicly accessible

What does the code in this PR do / what does it improve?

Related: XENONnT/outsource#93

In this PR, the rses_only restricted that the data_type can only be downloaded from the RSE in it.

Can you briefly describe how it works?

Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Notes on testing

• Until the automated tests pass, please mark the PR as a draft.
• On the XENONnT fork we test with database access, on private forks there is no database access for security considerations.

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[coveralls]

coverage: 90.379% (+0.02%) from 90.36%
when pulling 1874c62 on rucio_remote_backend_rses_only
into a412b43 on master.

[yuema137]

This PR adds an input to select available rses. Looks good to me