feat: add echo command

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.23810% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 90.67%. Comparing base (83e8621) to head (f1f8b59).

Files	Patch %	Lines
rsql_core/src/shell/repl.rs	0.00%	6 Missing :warning:
rsql_core/src/configuration.rs	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #55 +/- ## ========================================== + Coverage 90.38% 90.67% +0.29% ========================================== Files 45 46 +1 Lines 3899 4042 +143 ========================================== + Hits 3524 3665 +141 - Misses 375 377 +2 ```

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[github-actions[bot]]

Bencher

Report	Thu, March 21, 2024 at 01:08:14 UTC
Project	theseus-rs/rsql
Branch	add-echo-command
Testbed	localhost

Benchmark	Latency	Latency Results nanoseconds (ns)
version	➖ (view plot)	44656000.000

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