supports multiple harvesting stages (for farming:pepper)

[nixnoxus]

farming:pepper has 3 harvesting stages:

• stage 5 (green pepper)
• stage 6 (yellow pepper)
• stage 7 (red pepper)

See also: https://notabug.org/TenPlus1/farming/src/master/crops/pepper.lua#L114-L155

The bot only knows level 5 so far. With this PR stage 6 and 7 are also detected by the sensor and also harvested by the bot.

This change are successfully tested with Minetest 5.4.1 (and minetest_game) and 3x3 field with sensor. Each for:

• farmin:beanpole,
• farming:grapes,
• ethereal:onion,
• ethereal:strawberry,
• farming:rice,
• farming:wheat
• farming:pea
• farming:pepper

and this a sign_cmnd:

turn_right
harvest
sow_seed 1
move 3
exit

[nixnoxus]

thank you!