Restore STRALGO command reference, indicated support dropped in Redis 7

[amiramm]

I was looking for it today and found the STRALGO LCS page has been completely removed from reference documentation. Found it only in the Web archive https://web.archive.org/web/20210117130146/https://redis.io/commands/stralgo

Instead, a reference to the new command LCS, to be introduced in Redis 7, now appears.

I ask that we:

1. Maintain the previous command reference to STRALGO LCSand indicate the plan to drop support for it in Redis 7; link to the new command page. This will serve Redis 6 users for the foreseeable future.
2. Update the new LCS page to indicate the new command replaces STRALGO LCS to better facilitate migration to Redis 7