Overhaul tracker keys: allow permanent keys

[josecelano]

This PR introduces a new feature. Tracker keys can be permanent.

How to use the endpoint

Upload a pre-generated and expiring key

curl -X POST http://localhost:1212/api/v1/keys?token=MyAccessToken \
     -H "Content-Type: application/json" \
     -d '{
     	   "key": "Xc1L4PbQJSFGlrgSRZl8wxSFAuMa2110",
           "seconds_valid": 7200
         }'        

Upload a pre-generated and permanent key

curl -X POST http://localhost:1212/api/v1/keys?token=MyAccessToken \
     -H "Content-Type: application/json" \
     -d '{
     	   "key": "Xc1L4PbQJSFGlrgSRZl8wxSFAuMa2110",
           "seconds_valid": null
         }'        

Generate a random and expiring key

You can omit the key, and the tracker will generate a random one.

curl -X POST http://localhost:1212/api/v1/keys?token=MyAccessToken \
     -H "Content-Type: application/json" \
     -d '{
     	   "key": null,
           "seconds_valid": 7200
         }'        

Generate a random and permanent key

curl -X POST http://localhost:1212/api/v1/keys?token=MyAccessToken \
     -H "Content-Type: application/json" \
     -d '{
     	   "key": null,
           "seconds_valid": null
         }'        

NOTES

• Fields in the json object are mandatory. You cannot omit them. Instead of omitting the field, I've decided to use the null value to represent the case where the value is not needed. I prefer to use always the same structure and make it explicit. However, omitting the field could have other advantages, like requiring less maintenance. For example, if we rename a field (breaking change), that would not affect users who are not using that field.
• I've introduced manual database migrations. The second_valid column in the keys table is now nullable (for permanent keys).

[codecov]

Codecov Report

Attention: Patch coverage is 52.94118% with 96 lines in your changes missing coverage. Please review.

Project coverage is 76.89%. Comparing base (1fdf3a8) to head (c5beff5).

Files	Patch %	Lines
src/core/mod.rs	54.68%	29 Missing ⚠️
src/core/databases/mysql.rs	0.00%	25 Missing ⚠️
src/core/databases/sqlite.rs	41.93%	18 Missing ⚠️
src/core/auth.rs	72.72%	9 Missing ⚠️
src/core/error.rs	0.00%	7 Missing ⚠️
src/servers/apis/v1/context/auth_key/resources.rs	82.14%	5 Missing ⚠️
src/servers/apis/v1/context/auth_key/handlers.rs	83.33%	2 Missing ⚠️
src/servers/apis/v1/context/auth_key/forms.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #983      +/-   ##
===========================================
- Coverage    77.41%   76.89%   -0.52%     
===========================================
  Files          184      184              
  Lines         9812     9916     +104     
===========================================
+ Hits          7596     7625      +29     
- Misses        2216     2291      +75     

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[josecelano]

ACK c5beff5

[josecelano]

Hi @da2ce7, this is ready for review.