docs: fix broken Slack community link formatting

[LyannEpitech]

Summary

Fixes #5400

Corrects the Markdown link syntax in the LiteLLM documentation page. The link was incorrectly formatted as
(Slack community)[https://slack.keephq.dev] instead of [Slack community](https://slack.keephq.dev).

Changes

• Fixed reversed brackets/parentheses in Slack community link
• Changed from (text)[url] to [text](url) format

Affected file

• docs/deployment/local-llm/keep-with-litellm.mdx

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