dspace_statistics_api: Use f-strings instead of format()

We had previously been avoiding the f-strings because we needed to
run on Python 3.5 and they were only available in Python 3.6+, but
now the black formatter requires Python 3.6 and all our systems are
running Python 3.6+ anyways.

dspace_statistics_api/app.py

@@ -77,9 +77,7 @@ class ItemResource:
                 if cursor.rowcount == 0:
                     raise falcon.HTTPNotFound(
                         title="Item not found",
-                        description='The item with id "{}" was not found.'.format(
-                            str(item_id)
-                        ),
+                        description=f'The item with id "{str(item_id)}" was not found.',
                     )
                 else:
                     results = cursor.fetchone()

dspace_statistics_api/database.py

@@ -15,9 +15,7 @@ class DatabaseManager:
     """Manage database connection."""
 
     def __init__(self):
-        self._connection_uri = "dbname={} user={} password={} host={} port={}".format(
-            DATABASE_NAME, DATABASE_USER, DATABASE_PASS, DATABASE_HOST, DATABASE_PORT
-        )
+        self._connection_uri = f"dbname={DATABASE_NAME} user={DATABASE_USER} password={DATABASE_PASS} host={DATABASE_HOST} port={DATABASE_PORT}"
 
     def __enter__(self):
         try:

dspace_statistics_api/indexer.py

@@ -70,13 +70,13 @@ def get_statistics_shards():
 
     if len(statistics_core_years) > 0:
         # Begin building a string of shards starting with the default one
-        shards = "{}/statistics".format(SOLR_SERVER)
+        shards = f"{SOLR_SERVER}/statistics"
 
         for core in statistics_core_years:
             # Create a comma-separated list of shards to pass to our Solr query
             #
             # See: https://wiki.apache.org/solr/DistributedSearch
-            shards += ",{}/{}".format(SOLR_SERVER, core)
+            shards += f",{SOLR_SERVER}/{core}"
 
     # Return the string of shards, which may actually be empty. Solr doesn't
     # seem to mind if the shards query parameter is empty and I haven't seen
@@ -134,9 +134,7 @@ def index_views():
             while results_current_page <= results_num_pages:
                 # "pages" are zero based, but one based is more human readable
                 print(
-                    "Indexing item views (page {} of {})".format(
-                        results_current_page + 1, results_num_pages + 1
-                    )
+                    f"Indexing item views (page {results_current_page + 1} of {results_num_pages + 1})"
                 )
 
                 solr_query_params = {
@@ -219,9 +217,7 @@ def index_downloads():
             while results_current_page <= results_num_pages:
                 # "pages" are zero based, but one based is more human readable
                 print(
-                    "Indexing item downloads (page {} of {})".format(
-                        results_current_page + 1, results_num_pages + 1
-                    )
+                    f"Indexing item downloads (page {results_current_page + 1} of {results_num_pages + 1})"
                 )
 
                 solr_query_params = {