log panic full stack

[liguozhong]

What this PR does / why we need it:
log panic full stack.

This pr can't fix any issue directly, but it can provide a log the next time the panic occurs, the nil pointer bug is difficult to locate without a full stack

level=info ts=2022-10-13T08:10:35.236282467Z caller=index_set.go:422 table-name=loki_index_19278 file-name=loki-write-0-1664440320185296918-1665646200.gz msg="downloaded file" total_time=127.79166ms
level=info ts=2022-10-13T08:10:35.329011798Z caller=index_set.go:422 table-name=loki_index_19278 file-name=loki-write-0-1664440320185296918-1665631800.gz msg="downloaded file" total_time=220.608618ms
level=error ts=2022-10-13T08:10:35.341914548Z caller=index_set.go:265 table-name=loki_index_19278 msg="sync failed, retrying it" err="recovered from panic opening boltdb file: runtime error: invalid memory address or nil pointer dereference"
level=error ts=2022-10-13T08:10:35.341957794Z caller=index_set.go:104 table-name=loki_index_19278 msg="failed to initialize table loki_index_19278, cleaning it up" err="recovered from panic opening boltdb file: runtime error: invalid memory address or nil pointer dereference"
level=error ts=2022-10-13T08:10:35.341970873Z caller=table.go:294 table-name=loki_index_19278 msg="failed to init user index set " err="recovered from panic opening boltdb file: runtime error: invalid memory address or nil pointer dereference"
level=error ts=2022-10-13T08:10:35.341988856Z caller=table.go:312 table-name=loki_index_19278 org_id=fake msg="index set  has some problem, cleaning it up" err="recovered from panic opening boltdb file: runtime error: invalid memory address or nil pointer dereference"
level=error ts=2022-10-13T08:10:35.384714473Z caller=table.go:314 table-name=loki_index_19278 msg="failed to cleanup broken index set " err="unlinkat /var/loki/boltdb-shipper-cache/loki_index_19278/.nfs00000000002a1

Which issue(s) this PR fixes:
Fixes #7406

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide
• Documentation added
• Tests updated
• CHANGELOG.md updated
• Changes that require user attention or interaction to upgrade are documented in docs/sources/upgrading/_index.md

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[dannykopping]

@liguozhong you're on fire!