docs: fix filter docs to replace exact.

[winder]

Summary

The equal and exact types were merged in https://github.com/algorand/indexer/pull/1468 but the documentation was not properly updated. This PR updates the documentation to replace exact with equal.

[codecov[bot]]

Codecov Report

Merging #98 (97f5c50) into master (442791a) will increase coverage by 1.88%. The diff coverage is 76.19%.

:exclamation: Current head 97f5c50 differs from pull request most recent head d6f5d5e. Consider uploading reports for the commit d6f5d5e to get more accurate results

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
+ Coverage   67.66%   69.54%   +1.88%     
==========================================
  Files          32       36       +4     
  Lines        1976     2417     +441     
==========================================
+ Hits         1337     1681     +344     
- Misses        570      645      +75     
- Partials       69       91      +22     

Impacted Files	Coverage Δ
conduit/data/block_export_data.go	100.00% <ø> (+92.30%)	:arrow_up:
conduit/plugins/importers/algod/metrics.go	100.00% <ø> (ø)
...plugins/processors/filterprocessor/gen/generate.go	34.28% <ø> (ø)
pkg/cli/internal/list/list.go	20.75% <ø> (ø)
...lugins/exporters/postgresql/postgresql_exporter.go	65.68% <52.38%> (-12.52%)	:arrow_down:
pkg/cli/cli.go	65.97% <65.97%> (ø)
conduit/pipeline/pipeline.go	65.86% <73.28%> (+0.41%)	:arrow_up:
conduit/data/config.go	76.47% <76.47%> (ø)
conduit/plugins/importers/algod/algod_importer.go	90.51% <90.69%> (+2.20%)	:arrow_up:
conduit/pipeline/errors.go	100.00% <100.00%> (ø)
... and 4 more

... and 7 files with indirect coverage changes

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[winder]

Looks good thanks! Should expression-type be wrapped in quotes? I only see it being defined like this in conduit/plugins/processors/filterprocessor/README.md (which is a markdown file).

added quotes.