extend grep filter to accept microsecond precision in tags

[rptaylor]

In some cases the tag names can have extra precision in their timestamps. This extends the filter to accept a potential dot and up to 3 digits for microseconds.

Fix #3271

It works based on this simple test:

$ cat tags
generic-2023-05-04T22:00:25Z     │    13476 │ 4 May 2023 15:00:49  │        │ 
generic-2023-05-04T22:51:06Z     │    13478 │ 4 May 2023 15:51:27  │        │ 
generic-2023-05-05T21:20:12.918Z │    13480 │ 5 May 2023 14:20:13  │        │ 
generic-2023-05-07T15:05:56.115Z │    13481 │ 7 May 2023 08:05:57  │        │ 
# previous filter
$ grep -E  '^generic(_[[:digit:]]+)?-[[:digit:]]{4}-[[:digit:]]{2}-[[:digit:]]{2}T[[:digit:]]{2}:[[:digit:]]{2}:[[:digit:]]{2}Z' tags
generic-2023-05-04T22:00:25Z     │    13476 │ 4 May 2023 15:00:49  │        │ 
generic-2023-05-04T22:51:06Z     │    13478 │ 4 May 2023 15:51:27  │        │ 
# updated filter
$ grep -E '^generic(_[[:digit:]]+)?-[[:digit:]]{4}-[[:digit:]]{2}-[[:digit:]]{2}T[[:digit:]]{2}:[[:digit:]]{2}:[[:digit:]]{2}\.?[[:digit:]]{0,3}Z' tags
generic-2023-05-04T22:00:25Z     │    13476 │ 4 May 2023 15:00:49  │        │ 
generic-2023-05-04T22:51:06Z     │    13478 │ 4 May 2023 15:51:27  │        │ 
generic-2023-05-05T21:20:12.918Z │    13480 │ 5 May 2023 14:20:13  │        │ 
generic-2023-05-07T15:05:56.115Z │    13481 │ 7 May 2023 08:05:57  │        │ 

[cernvm-bot]

Can one of the admins verify this patch?

[rptaylor]

@HereThereBeDragons this is an important fix required for GC to run in our environment, could we get it in 2.11 or a 2.10.x ?

[jblomer]

@cernvm-bot cloudtest

[cernvm-bot]

building for cloudtests finished: SUCCESS
https://lcgapp-services.cern.ch/cvmfs-jenkins/job/CvmfsFullBuildDocker/3914/

[cernvm-bot]

cloudtests finished: FAILURE
https://lcgapp-services.cern.ch/cvmfs-jenkins/job/CvmfsCloudTesting/1734/

[vvolkl]

@cernvm-bot cloudtest

[cernvm-bot]

building for cloudtests finished: SUCCESS
https://lcgapp-services.cern.ch/cvmfs-jenkins/job/CvmfsFullBuildDocker/3919/

[cernvm-bot]

cloudtests finished: FAILURE
https://lcgapp-services.cern.ch/cvmfs-jenkins/job/CvmfsCloudTesting/1748/

[vvolkl]

Test failure unrelated