Feature request: Create an Electric index for like/ilike ops in shape's WHERE clause

[alco]

Electric has indexes for the equality op (WHERE <table_field> = <const>) and array inclusion op (WHERE <array_field> @> <const_array>).

Electric could use an index implementation that would speed up LIKE and ILIKE ops that are often used for matching on string fields. As seen in https://github.com/electric-sql/electric/pull/2895, adding row filters on the Postgres publication for WHERE clauses containing ILIKE offers a noticeable performance boost when matching incoming transactions to active shapes. With row filtering disabled, Electric needs to have its own similar index implementation to maintain the same performance characteristics