Allow exclude files

[rubensa]

I have configured:

        // Determines if the linter will lint the workspaces on startup and configuration changes.
        "sqlfluff.linter.lintEntireProject": true,

So, when I open a project, all sql files are parsed.

The problem here is that "all" files are parsed and, in my case, some of them are generated copies "on the fly" from the original ones.

I have a Java project with some sql file in the class path. When I open the project those files are copied to target/classes folder (which is also removed before re-generated).
This makes an error for sqlfluff parsing files from a directory that, suddenly, does not exists.

It should be great to have an option, similar to files.exclude, that allows excluding files and directories from being parsed by sqlfluff.

[rubensa]

This is an example of the error messages reported in the SQLFluff output:

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Reading from workspace, not stdin

--------------------Executing Command--------------------

/opt/conda/envs/dev/bin/sqlfluff lint --format json --exclude-rules RF01

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Received close event, code 1 signal null
Raw stdout output:

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Raw stderr output:

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Traceback (most recent call last):
  File "/opt/conda/envs/dev/bin/sqlfluff", line 8, in <module>
    sys.exit(cli())
             ^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/cli/commands.py", line 633, in lint
    result = lnt.lint_paths(
             ^^^^
^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/linter/linter.py", line 1084, in lint_paths
    for i, linted_file in enumerate(runner.run(expanded_paths, fix), start=1):
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/linter/runner.py", line 107, in run
    for fname, partial in self.iter_partials(fnames, fix=fix):
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/linter/runner.py", line 60, in iter_partials
    for fname, rendered in self.iter_rendered(fnames):
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/linter/runner.py", line 47, in iter_rendered
    yield fname, self.linter.render_file(fname, self.config)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/linter/linter.py", line 751, in render_file
    raw_file, config, encoding = self.load_raw_file_and_config(fname, root_config)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/linter/linter.py", line 120, in load_raw_file_and_config
    encoding = get_encoding(fname=fname, config=file_config)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/envs/dev/lib/python3.11/site-packages/sqlfluff/core/file_helpers.py", line 13, in get_encoding
    with open(fname, "rb") as f:
         ^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/workspaces/sample/target/test-classes/cleanup.sql'


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