From: Jaydeep Das <jaydeepjd.8914@gmail.com>

Add new helper function `gpg_trust_level_to_str()` which will
convert a given member of `enum signature_trust_level` to its
corresponding string (in lowercase). For example, `TRUST_ULTIMATE`
will yield the string "ultimate".

This will abstract out some code in `pretty.c` relating to gpg
signature trust levels.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: Jaydeep Das <jaydeepjd.8914@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.1281.v3.git.1657341817595.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1281.git.1657202265048.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.1281.v2.git.1657279447515.gitgitgadget@gmail.com