Fix spellchecker

[zuiderkwast]

The spellchecker works as described in the README.md, but there are some problems:

• The spellchecker ignores text within backticks, but many command arguments and similar are not written in backticks, so they are reported as spelling errors. Solution: Add backticks for these.
• Our config file is .spellcheck.yml but according to https://www.npmjs.com/package/spellchecker-cli it needs to be called .spellcheckerrc.yml.
• Some words need to be added to the wordlist. Regexes can be used. For example ValkeyModule.*.
• Probably there are some actual spelling errors that need to be corrected.