docs: performance improvments for running Renovate

[jamietanna]

• which cache(s) should be persistent?
  • related: docs(cache): add more information on the different cache(s) and what gets used where #41456
• what can you do with Host Rules to make things more efficient?
• how to debug slow-running repos?
  • debug logs
  • OTel
• what are some of the common performance issues?