nimbus-era-files: role for ERA generating timer

https://github.com/status-im/infra-nimbus/issues/98

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ansible/roles/nimbus-era-files/README.md

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+# Description
+
+This role configures a Systemd timer which generates Nimbus ERA files weekly.
+
+The purpose of those is to save space by sharing the same historical data between nodes.
+
+Read more about ERA files [here](https://github.com/status-im/nimbus-eth2/blob/unstable/docs/e2store.md#era-files).
+
+# Configuration
+
+```yaml
+nimbus_era_files_timer_name: 'nimbus-era-files-update'
+nimbus_era_files_timer_path: '/data/era'
+nimbus_era_files_nclidb_path: '/data/nimbus/repo/build/bin/ncli_db'
+nimbus_era_files_db_path: '/data/nimbus/data/db'
+```
+
+# Management
+
+The timer runs weekly with 12h random delay by default, but you can start it manually:
+```
+ > systemctl -o cat status nimbus-era-files-update
+● nimbus-era-files-update.service - Update Nimbus beacon node ERA files
+     Loaded: loaded (/etc/systemd/system/nimbus-era-files-update.service; static; vendor preset: enabled)
+     Active: inactive (dead) since Wed 2022-07-13 20:22:16 UTC; 2h 31min ago
+TriggeredBy: ● nimbus-era-files-update.timer
+       Docs: https://github.com/status-im/infra-role-systemd-timer
+    Process: 153635 ExecStart=/data/beacon-node-mainnet-stable-01/repo/build/ncli_db exportEra --db=/data/beacon-node-mainnet-stable-01/data/shared_mainnet_0/db (code=exited, status=0/SUCCESS)
+   Main PID: 153635 (code=exited, status=0/SUCCESS)
+
+Written all complete eras
+All time are ms
+     Average,       StdDev,          Min,          Max,      Samples,         Test
+     565.673,       41.529,      486.430,      635.203,           45, tState
+    1107.374,      147.118,      685.914,     1293.401,           45, tBlocks
+nimbus-era-files-update.service: Succeeded.
+Finished Update Nimbus beacon node ERA files.
+```

ansible/roles/nimbus-era-files/defaults/main.yml

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+---
+nimbus_era_files_timer_name: 'nimbus-era-files-update'
+nimbus_era_files_timer_path: '/data/era'
+nimbus_era_files_timer_user: 'nimbus'
+nimbus_era_files_timer_group: 'staff'
+nimbus_era_files_timer_frequency: 'weekly'
+nimbus_era_files_timer_timeout_sec: 82800
+nimbus_era_files_timer_random_delay_sec: '{{ 60 * 60 * 12 }}'
+nimbus_era_files_timer_ionice_class: 'idle'
+nimbus_era_files_timer_script: '{{ nimbus_era_files_timer_path }}/update.sh'
+
+# Mandatory
+#nimbus_era_files_nclidb_path: ~
+#nimbus_era_files_db_path: ~

ansible/roles/nimbus-era-files/tasks/main.yml

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+---
+- name: Create ERA files directory
+  file:
+    path: '{{ nimbus_era_files_timer_path }}'
+    owner: '{{ nimbus_era_files_timer_user }}'
+    group: '{{ nimbus_era_files_timer_group }}'
+    state: 'directory'
+
+- name: Create timer for ERA file updates
+  include_role: name=systemd-timer
+  vars:
+    systemd_timer_description:       'Update Nimbus beacon node ERA files'
+    systemd_timer_start_on_creation: false
+    systemd_timer_name:              '{{ nimbus_era_files_timer_name }}'
+    systemd_timer_user:              '{{ nimbus_era_files_timer_user }}'
+    systemd_timer_group:             '{{ nimbus_era_files_timer_group }}'
+    systemd_timer_frequency:         '{{ nimbus_era_files_timer_frequency }}'
+    systemd_timer_random_delay_sec:  '{{ nimbus_era_files_timer_random_delay_sec }}'
+    systemd_timer_timeout_sec:       '{{ nimbus_era_files_timer_timeout_sec }}'
+    systemd_timer_ionice_class:      '{{ nimbus_era_files_timer_ionice_class }}'
+    systemd_timer_work_dir:          '{{ nimbus_era_files_timer_path }}'
+    systemd_timer_script_path:       '{{ nimbus_era_files_nclidb_path }}'
+    systemd_timer_script_args:       'exportEra --db={{ nimbus_era_files_db_path }}'