add / update fstab entry with --update-fstab

[timfeirg]

• abs path check for sqlite and similars
• correctly handle slice arguments, even though they don't exist in juicefs mount yet
• do not run in containers
• unit tests

PR code will produce the following result:

closes #2432

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #2446 (d2ffbbc) into main (c274542) will decrease coverage by 0.14%.
The diff coverage is 5.71%.

❗ Current head d2ffbbc differs from pull request most recent head 9df976f. Consider uploading reports for the commit 9df976f to get more accurate results

@@            Coverage Diff             @@
##             main    #2446      +/-   ##
==========================================
- Coverage   61.59%   61.45%   -0.15%     
==========================================
  Files         137      137              
  Lines       25563    25633      +70     
==========================================
+ Hits        15746    15752       +6     
- Misses       7970     8033      +63     
- Partials     1847     1848       +1     

Impacted Files	Coverage Δ
cmd/mount.go	49.85% <0.00%> (-11.88%)	⬇️
cmd/mount_unix.go	49.56% <100.00%> (+1.81%)	⬆️
pkg/chunk/utils_unix.go	73.33% <0.00%> (-20.00%)	⬇️
pkg/chunk/disk_cache.go	81.35% <0.00%> (ø)
pkg/meta/redis.go	72.01% <0.00%> (+0.04%)	⬆️
pkg/meta/sql.go	66.00% <0.00%> (+0.09%)	⬆️
pkg/chunk/cached_store.go	77.56% <0.00%> (+0.17%)	⬆️
pkg/meta/tkv_mem.go	88.43% <0.00%> (+0.57%)	⬆️

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[timfeirg]

close in favor of #2462