fix: allow indexers to have workspace

[cristianmtr]

We want to allow setting of workspace in Indexers without name.

Brought up in #1380 , when tried setting meta={'workspace': tmpdir} but I get an error

like so

with BinaryPbIndexer('pbdix.bin', metas={'workspace': tmpdir.strpath}) as idxer:

(<class 'AttributeError'>, AttributeError("'BinaryPbIndexer' object has no attribute 'warn_unnamed'"), <traceback object at 0x7f243731fec0>)

Copying the approach from here worked https://github.com/jina-ai/jina/blob/008638d3e61c20c585b376ea003be712123a6eb2/tests/unit/executors/indexers/test_numpyindexer.py#L39

metas = {
        'is_trained': False,
        'is_updated': False,
        'batch_size': None,
        'workspace': f'{tmpdir}',
        'name': None,
        'on_gpu': False,
        'warn_unnamed': False,
        'max_snapshot': 0,
        'py_modules': None,
        'pea_id': '{root.metas.pea_id}',
        'separated_workspace': '{root.metas.separated_workspace}',
    }
    # FIXME how to open a specific file in a dir. os.path.join(tmpdir, file) doesn't work
    with BinaryPbIndexer('pbidx', metas=metas) as idxer:

Now the idx files are stored in the tmpdir, instead of the curdir.

Seems like the issue is with 'warn_unnamed': False,

[codecov]

Codecov Report

Merging #1383 (fe599ab) into master (be1d5b7) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1383      +/-   ##
==========================================
+ Coverage   83.45%   83.49%   +0.04%     
==========================================
  Files         103      103              
  Lines        6792     6792              
==========================================
+ Hits         5668     5671       +3     
+ Misses       1124     1121       -3     

Impacted Files	Coverage Δ
jina/drivers/querylang/select.py	79.31% <0.00%> (-6.90%)	⬇️
jina/peapods/grpc_asyncio.py	80.61% <0.00%> (+5.10%)	⬆️

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